Symmetry-adapted Perturbation Theory Research Articles

Ab initio dispersion potentials based on physics-based functional forms with machine learning.

In this study, we introduce SAPT10K, a comprehensive dataset comprising 9982 noncovalent interaction energies and their binding energy components (electrostatics, exchange, induction, and dispersion) for diverse intermolecular complexes of 944 unique dimers. These complexes cover significant portions of the intermolecular potential energy surface and were computed using higher-order symmetry-adapted perturbation theory, SAPT2+(3)(CCD), with a large aug-cc-pVTZ basis set. The dispersion energy values in SAPT10K serve as crucial inputs for refining the abinitio dispersion potentials based on Grimme's D3 and many-body dispersion (MBD) models. Additionally, Δ machine learning (ML) models based on newly developed intermolecular features, which are derived from intermolecular histograms of distances for element/substructure pairs to simultaneously account for local environments as well as long-range correlations, are also developed to address deficiencies of the D3/MBD models, including the inflexibility of their functional forms, the absence of MBD contributions in D3, and the standard Hirshfeld partitioning scheme used in MBD. The developed dispersion models can be applied to complexes involving a wide range of elements and charged monomers, surpassing other popular ML models, which are limited to systems with only neutral monomers and specific elements. The efficient D3-ML model, with Cartesian coordinates as the sole input, demonstrates promising results on a testing set comprising 6714 dimers, outperforming another popular ML model, component-based machine-learned intermolecular force field (CLIFF), by 1.5 times. These refined D3/MBD-ML models have the capability to replace the time-consuming dispersion components in symmetry-adapted perturbation theory-based calculations and can promptly illustrate the dispersion contribution in noncovalent complexes for supramolecular assembly and chemical reactions.

Beyond isotropic repulsion: Classical anisotropic repulsion by inclusion of p orbitals.

Accurate modeling of intermolecular repulsion is an integral component in force field development. Although repulsion can be explicitly calculated by applying the Pauli exclusion principle, this approach is computationally viable only for systems of limited sizes. Instead, it has previously been shown that repulsion can be reformulated in a "classical" picture: the Pauli exclusion principle prohibits electrons from occupying the same state, leading to a depletion of electronic charge between atoms, giving rise to an enhanced nuclear-nuclear electrostatic repulsion. This classical picture is called the isotropic S2/R approximation, where S is the overlap and R is the interatomic distance. This approximation accurately captures the repulsion of isotropic atoms such as noble gas dimers; however, a key deficiency is that it fails to capture the angular dependence of the repulsion of anisotropic molecules. To include directionality, the wave function must at least be a linear combination of s and p orbitals. We derive a new anisotropic S2/R repulsion model through the inclusion of the anisotropic p orbital term in the total wave function. Because repulsion is pairwise and decays rapidly, it can be truncated at a short range, making it amenable for efficient calculation of energy and forces in complex biomolecular systems. We present a parameterization of the S101 dimer database against the abinitio benchmark symmetry-adapted perturbation theory, which yields an rms error of only 0.9 kcal/mol. The importance of the anisotropic term is demonstrated through angular scans of water-water dimers and dimers involving halobenzene. Simulation of liquid water shows that the model can be computed efficiently for realistic system sizes.

An efficient method by combining different basis sets and SAPT levels.

In symmetry-adapted perturbation theory (SAPT), accurate calculations on non-covalent interaction (NCI) for large complexes with more than 50 atoms are time-consuming using large basis sets. More efficient ones with smaller basis sets usually result in poor prediction in terms of dispersion and overall energies. In this study, we propose two composite methods with baseline calculated at SAPT2/aug-cc-pVDZ and SAPT2/aug-cc-pVTZ with dispersion term corrected at SAPT2+ level using bond functions and smaller basis set with MP2 corrections respectively. Benchmark results on representative NCI data sets, such as S22, S66, and so forth, show significant improvements on the accuracy compared to the original SAPT Silver standard and comparable to SAPT Gold standard in some cases with much less computational cost.

A Rotational Study of 2-tert-Butylphenol and Its 1 : 1 Argon Complex.

The chirped-pulse Fourier Transform microwave spectrum of 2-tert-butylphenol, an industrial intermediate for the production of antioxidants, has been investigated in the 2-8 GHz frequency range. The spectral analysis has allowed obtaining precise structural information on the most stable conformer and its complex with argon. The conformation of the monomer reveals that the hydroxyl group is coplanar with the ring but points in the opposite direction to the tert-butyl group, reducing steric interactions. In the tert-butyl group one methyl group is coplanar and the other two are symmetrically staggered respect to the ring. The complex shows the rare gas sitting above the aromatic ring. Interestingly, neither the monomer nor the complex exhibit large-amplitude hydroxyl torsion motions, previously observed in 2,6-disubstituted phenols such as 2,6-di-tert-butylphenol or propofol. The experimental results are supported by computational calculations, validating the molecular structure. Additionally, symmetry-adapted perturbation theory has allowed determining the van der Waals intermolecular interaction energy of the complex.

Enantioselectivity from inelastic electron tunnelling through a chiral sensor

The vibration theory of olfaction, which explains it as the sensing of odorant molecules by their vibrational energies through inelastic electron tunnelling spectroscopy (IETS) has inspired olfactory sensor ideas. However, this theory has been presumed inadequate to explain the difference in smell between enantiomers (chiral molecules, which are mirror images of each other), since these have identical vibrational spectra. Going beyond phenomenological assumptions of enantioselective tunnelling, we show on the basis of ab initio modelling of real chiral molecules, that this drawback is indeed obviated for IETS-based olfactory sensors if they are chiral. Our treatment unifies IETS with chirality induced spin selectivity, which explains that charge polarization in chiral molecules by accompanied by spin polarization. First, we apply ab initio symmetry adapted perturbation theory to explain and illustrate enantioselective coupling of chiral odorant molecules and chiral olfactory sensors. This naturally leads to enantioselective coupling of the vibrational mode of an odorant to electron transport (electron-vibron coupling) in an IETS-based sensor when both odorant and sensor are chiral. Finally, we show, from phenomenological quantum transport calculations, that that in turn results in enantioselective IET spectra. Thus, we have demonstrated the feasibility of enantioselective sensing within a vibration framework. Our work also limns the possibility of quantum biomimetic electronic nose sensors that are enantioselective, a feature which could open up new sensing applications.

Water Potential from Adaptive Force Matching for Ice and Liquid with Revised Dispersion Predicts Supercooled Liquid Anomalies in Good Agreement with Two Independent Experimental Fits.

A revised version of the Water potential from Adaptive force matching for Ice and Liquid (WAIL) was developed by using the previous data set for fitting the WAIL model but with a dispersion term calculated using symmetry adapted perturbation theory (SAPT). The model has no adjustable parameters and relies solely on fitting first-principles information. The new model, named revised WAIL (rWAIL), shows improved predictions of most properties of water when compared to the previously published WAIL model. The rWAIL model also compares favorably to other first-principles-derived water models, such as MB-Pol, at only a fraction of the computational cost. The rWAIL model is used to study the properties of supercooled water. The model shows evidence of a liquid-liquid phase transition (LLPT) in the supercooled regimes with the liquid-liquid critical point (LLCP) at 203 K and 90 MPa. This estimate is in good agreement with a recent polynomial fit to the experimental density of water. Also, the fit to the surface tension of supercooled water based on the rWAIL model shows excellent agreement with the corresponding fit to the experimental data. Consistent with previously published molecular dynamics and experimental data, the surface tension of water exhibits exponential growth in the supercooled regime, which is likely a result of the emergence of a low-density liquid form of water. The simulation thus unites two separate experimental fits with one first-principles-based model, lending strong evidence of an LLPT in real water.

Impact of Combination Rules, Level of Theory, and Potential Function on the Modeling of Gas- and Condensed-Phase Properties of Noble Gases.

The systems of noble gases are particularly instructive for molecular modeling due to the elemental nature of their interactions. They do not normally form bonds nor possess a (permanent) dipole moment, and the only forces determining their bonding/clustering stems from van der Waals forces─dispersion and Pauli repulsion, which can be modeled by empirical potential functions. Combination rules, that is, formulas to derive parameters for pair potentials of heterodimers from parameters of corresponding homodimers, have been studied at length for the Lennard-Jones 12-6 potentials but not in great detail for other, more accurate, potentials. In this work, we examine the usefulness of nine empirical potentials in their ability to reproduce quantum mechanical (QM) benchmark dissociation curves of noble gas dimers (He, Ne, Ar, Kr, and Xe homo- and heterodimers), and we systematically study the efficacy of different permutations of combination relations for each parameter of the potentials. Our QM benchmark comprises dissociation curves computed by several different coupled cluster implementations as well as symmetry-adapted perturbation theory. The two-parameter Lennard-Jones potentials were decisively outperformed by more elaborate potentials that sport a 25-30 times lower root-mean-square error (RMSE) when fitted to QM dissociation curves. Very good fits to the QM dissociation curves can be achieved with relatively inexpensive four- or even three-parameter potentials, for instance, the damped 14-7 potential (Halgren, J. Am. Chem. Soc. 1992, 114, 7827-7843), a four-parameter Buckingham potential (Werhahn et al., Chem. Phys. Lett. 2015, 619, 133-138), or the three-parameter Morse potential (Morse, Phys. Rev. 1929, 34, 57-64). Potentials for heterodimers that are generated from combination rules have an RMSE that is up to 20 times higher than potentials that are directly fitted to the QM dissociation curves. This means that the RMSE, in particular, for light atoms, is comparable in magnitude to the well-depth of the potential. Based on a systematic permutation of combination rules, we present one or more combination rules for each potential tested that yield a relatively low RMSE. Two new combination rules are introduced that perform well, one for the van der Waals radius σij as and one for the well-depth ϵij as . The QM data and the fitted potentials were evaluated in the gas phase against experimental second virial coefficients for homo- and heterodimers, the latter of which allowed evaluation of the combination rules. The fitted models were used to perform condensed phase molecular dynamics simulations to verify the melting points, liquid densities at the melting point, and the enthalpies of vaporization produced by the models for pure substances. Subtle differences in the benchmark potentials, in particular, the well-depth, due to the level of theory used were found here to have a profound effect on the macroscopic properties of noble gases: second virial coefficients or the bulk properties in simulations. By explicitly including three-body dispersion in molecular simulations employing the best pair potential, we were able to obtain accurate melting points as well as satisfactory densities and enthalpies of vaporization.

Theoretical investigation of the nature of hydrogen bonds and cooperativity effect in methanol-water and ethanol-water clusters

ABSTRACT This study aims to cast light on the nature of hydrogen bonds and their cooperativity that exists in alcohol-water ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) ) (n = 1–10) clusters using atoms in molecules (AIM) theory and symmetry-adapted perturbation theory (SAPT). The investigation of optimum structures suggests that alcohol ( ROH ) forms two hydrogen bonds, one primary hydrogen bond ( O − H ⋅ ⋅ ⋅ O ) , and one secondary hydrogen bond ( C − H ⋅ ⋅ ⋅ O ) Two types of hydrogen bonds are addressed in these studies, where alcohol works as the hydrogen bond donor ( ROH ⋅ ⋅ ⋅ O H 2 ) and hydrogen bond acceptor ( RHO ⋅ ⋅ ⋅ HOH ) . The AIM results reveal that RHO ⋅ ⋅ ⋅ HOH and ROH ⋅ ⋅ ⋅ O H 2 hydrogen bonds are partially covalent. The SAPT study demonstrates that in all the clusters studied herein, the electrostatic interaction between alcohol and water is the main attractive force, and its contribution may be two times larger than the separate corresponding contributions from the dispersion and the induction terms. The electron density (ρ) at the bond critical point (BCP) is a suitable parameter to assess the strength of the interaction. The current study shows the strength and nature of ROH ⋅ ⋅ ⋅ O H 2 and RHO ⋅ ⋅ ⋅ HOH hydrogen bond, and cooperative effect in ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) .) (n = 1–10).

σ-Hole Site-Based Interactions within Hypervalent Pnicogen, Halogen, and Aerogen-Bearing Molecules with Lewis Bases: A Comparative Study.

σ-Hole site-based interactions in the trigonal bipyramidal geometrical structure of hypervalent pnicogen, halogen, and aerogen-bearing molecules with pyridine and NCH Lewis bases (LBs) were comparatively examined. In this respect, the ZF5···, XF3O2···, and AeF2O3···LB complexes (where Z = As, Sb; X = Br, I; Ae = Kr, Xe; and LB = pyridine and NCH) were investigated. The electrostatic potential (EP) analysis affirmations outlined the occurrence of σ-holes on the systems under consideration with disparate magnitudes that increased according to the following order: AeF2O3 < XF3O2 < ZF5. In line with EP outcomes, the proficiency of σ-hole site-based interactions increased as the atomic size of the central atom increased with a higher favorability for the pyridine-based complexes over NCH-based ones. The interaction energy showed the most favorable negative values of -35.97, -44.53, and -56.06 kcal/mol for the XeF2O3···, IF3O2···, and SbF5···pyridine complexes, respectively. The preferentiality pattern of the studied interactions could be explained as a consequence of (i) the dramatic rearrangement of ZF5 molecules from the trigonal bipyramid geometry to the square pyramidal one, (ii) the significant and tiny deformation energy in the case of the interaction of XF3O2 molecules with pyridine and NCH, respectively, and (iii) the absence of geometrical deformation within the AeF2O3···pyridine and ···NCH complexes other than the XeF2O3···pyridine one. Quantum theory of atoms in molecules and noncovalent interaction index findings reveal the partially covalent nature of most of the investigated interactions. Symmetry-adapted perturbation theory affirmations declared that the electrostatic component was the driving force beyond the occurrence of the considered interactions. The obtained findings will help in improving our understanding of the effect of geometrical deformation on intermolecular interactions.

Screening of toluene absorbents based on molecular simulation and experimental investigation on novel compound solvents

This work aims to screen out absorbents with excellent performance to control toluene pollution. Based on density functional theory (DFT), this article calculated the binding energy between toluene and organic solvents molecules with specific functional groups, and comprehensively examined the physical and chemical properties of the solvents to screen out suitable toluene absorbents. The computational binding energy and the experimental absorption efficiency have the same change tendency, that is, the value of the binding energy determines the ability of the solvents to absorb toluene. Pentaethylene glycol dimethyl ether (PGDE), 1-methyl-2-pyrrolidinone (NMP), dioctyl phthalate (DOP) and sulfolane (SUL) were initially selected as toluene absorbents. Atoms in molecules (AIM) analysis, reduced density gradient (RDG) analysis and symmetry-adapted perturbation theory (SAPT) analysis were used to explore the microscopic mechanism of toluene absorption by four organic solvents. The results show that the interactions between organic solvents and toluene are weak interactions dominated by dispersion attraction. The experiment used polyethylene glycol dimethyl ether (NHD) with very low volatility as the main solvent, which is a polymer containing the main component PGDE, and compounded it with NMP, DOP, and SUL respectively. The absorption experiment investigated the efficiency of compound solvents with different mass fractions of compound components on toluene under the conditions of normal pressure, liquid-to-gas ratio 2.5 L/m3, gas flow rate 4 L/min, temperature 30°C, inlet concentration approximately 6000 mg/m3, and packing height 60 cm. The results show that the toluene absorption efficiency of the three compound solvents is more than 91%. Considering the absorption performance, consumption and stability of the solvent, NHD-SUL solvent (20 wt.% SUL) was finally selected as the new compound solvent. The new compound solvent regenerated lean solution still maintains a good absorption efficiency of 90% after 13 desorption cycles. Theoretical and experimental research are of great significance for the future treatment of exhaust gas pollution.

New Aspects of Alcohol-Alcohol and Alcohol-Water Interactions: Crystallographic and Quantum Chemical Studies of Antiparallel O-H/O-H Interactions.

New modes of interaction, antiparallel O-H/O-H interactions of alcohol-alcohol dimers and alcohol-water dimers, were studied by analyzing data in the Cambridge Structural Database (CSD) and by calculating potential energy surfaces at a very accurate quantum chemical CCSD(T)/CBS level. The data reveal the existence of antiparallel interactions in crystal structures and significant interaction energies. Data from the CSD for alcohol-alcohol dimers show 49.2% of contacts with classical hydrogen bonds and 10.1% of contacts with antiparallel interactions, while for alcohol-water dimers, 59.4% of contacts are classical hydrogen bonds and only 0.6% of contacts are antiparallel interactions. The calculations were performed on methanol, ethanol, and n-propanol dimers. Classical hydrogen-bonded alcohol-alcohol and alcohol-water dimers have interaction energies of up to -6.2 kcal/mol and up to -5.5 kcal/mol, respectively. Antiparallel interactions in alcohol-alcohol and alcohol-water dimers have interaction energies of up to -4.7 kcal/mol and up to -4.4 kcal/mol, respectively. Symmetry-adapted perturbation theory analysis for antiparallel interactions shows their electrostatic nature.

Second quantization-based symmetry-adapted perturbation theory: Generalizing exchange beyond single electron pair approximation.

This paper presents a general second-quantized form of a permutation operator interchanging n pairs of electrons between interacting subsystems in the framework of the symmetry-adapted perturbation theory (SAPT). We detail the procedure for constructing this operator through the consecutive multiplication of single-pair permutation operators. This generalized form of the permutation operator has enabled the derivation of universal formulas for S2n approximations of the exchange energies in the first and second order of the interaction operator. We present expressions for corrections of S4 approximations and assess its efficacy on a selection of systems anticipated to exhibit a slowly converging overlap expansion. Additionally, we outline a method to sum the overlap expansion series to infinity in second-quantization, up to the second order in V. This new approach offers an alternative to the existing formalism based on density-matrix formulations. When combined with a symbolic algebra program for automated derivations, it paves the way for advancements in SAPT theory, particularly for intricate wavefunction theories.

Exploring the conformational landscape, hydrogen bonding, and internal dynamics in the diallyl ether and diallyl sulfide monohydrates.

The conformational spaces of the diallyl ether (DAE) and diallyl sulfide (DAS) monohydrates were explored using rotational spectroscopy from 6 to 19GHz. Calculations at the B3LYP-D3(BJ)/aug-cc-pVTZ level suggested significant differences in their conformational behavior, with DAE-w exhibiting 22 unique conformers and DAS-w featuring three stable structures within 6 kJ mol-1. However, only transitions from the lowest energy conformer of each were experimentally observed. Spectral analysis confirmed that binding with water does not alter the conformational preference for the lowest energy structure of the monomers, but it does influence the relative stabilities of all other conformers, particularly in the case of DAE. Non-covalent interaction and quantum theory of atoms in molecules analyses showed that the observed conformer for each complex is stabilized by two intermolecular hydrogen bonds (HBs), where water primarily interacts with the central oxygen or sulfur atom of the diallyl compounds, along with secondary interactions involving the allyl groups. The nature of these interactions was further elucidated using symmetry-adapted perturbation theory, which suggests that the primary HB interaction with S in DAS is weaker and more dispersive in nature compared to the primary HB in DAE. This supports the experimental observation of a tunneling splitting exclusively in the rotational spectrum of DAS-w, as the weaker contact allows water to undergo internal motions within the complex, as shown based on calculated transition state structures for possible tunneling pathways.

DFT-D3 and TD-DFT studies on the sensor performance of the functionalized carbon quantum dots for curcumin

In the present study, the interaction of curcumin molecule with a series of functionalized carbon quantum dots (f-CQDs, f=-OH, -NH2, -COOH) was investigated for drug sensing purposes by using density functional theory (DFT) calculations. After functionalization, the adsorption capacity of CQDs for curcumin was improved to a certain extent. The quantum theory of atoms in molecules (QTAIM) and symmetry-adapted perturbation theory (SAPT) energy decomposition revealed that the dispersion force played a dominant role in the stabilizing. The energy gap of the CQDs was reduced through functionalization. The adsorption of curcumin led to a significant energy gap change especially for CQDs with -COOH functionalized (-21.39 %), suggesting its promising sensor performance to curcumin. The detection ability of CQDs and f-CQDs for curcumin was further assessed by simulating the ultra-violet visible (UV–vis) and infrared (IR) spectra.

Uracil-water interaction revisited - in search of single H-bonded secondary minima.

Monohydrated uracil (UW) complexes are stabilized by both O⋯HO and NH⋯O hydrogen bonds (H-bonds), simultaneously participating in forming three stable cyclic structures. The role and contribution of these individual H-bonds (O⋯HO and NH⋯O) to the stability of the three UW complexes are still not understood, because of the technical problems in obtaining their optimized structures by standard geometry optimization. The present study explores a non-standard approach to identify three single H-bonded local minima structures without imaginary frequency using DFT (M06-2X, B3LYP and B3LYP-D3), MP2 and CCSD(T) theories and Dunning's correlation-consistent aug-cc-pVTZ basis set, in both vacuum and aqueous media (CPCM method). The results reveal that these new structures are very shallow secondary minima between two deep wells or next to a deep well of primary minima (double H-bonded structures) in the potential energy surface. The H-bond energy of these single H-bonded complexes is found to be less sensitive to a wide range (about 15-20 degrees) of O⋯HO and NH⋯O angles, and the linearity is preferred in the stable three single H-bonded structures. The technical method used to locate such a shallow minimum is described in detail and may be useful for identifying local minima in other cases where consecutive multiple H-bonded structures are global minima. Energy decomposition (using symmetry adapted perturbation theory (SAPT)) of interaction energy, electron redistribution, and relevant vibrational modes are discussed.

Aluminium phosphide (Al12P12) nanocage as a potential sensor for volatile organic compounds: A DFT study.

The efficacy of aluminium phosphide (Al12P12) nanocage toward sensing methanol (MeOH) and ethanol (EtOH) volatile organic compounds (VOCs) was herein thoroughly elucidated utilizing various density functional theory (DFT) computations. In this perspective, MeOH⋯ and EtOH⋯Al12P12 complexes were investigated within all plausible configurations. According to the energetic features, the EtOH⋯Al12P12 complexes exhibited larger negative values of adsorption and interaction energies with values up to -27.23 and -32.84 kcal mol-1, respectively, in comparison to the MeOH⋯Al12P12 complexes. Based on the symmetry-adapted perturbation theory (SAPT) results, the electrostatic forces were pinpointed as the predominant component beyond the adsorption process within the preferable MeOH⋯ and EtOH⋯Al12P12 complexes. The findings of the noncovalent interaction (NCI) index and quantum theory of atoms in molecules (QTAIM) outlined the closed-shell nature of the interactions within the studied complexes. Substantial variations were found in the molecular orbitals distribution patterns of MeOH/EtOH molecules and Al12P12 nanocage, outlining the occurrence of the adsorption process within the complexes under investigation. Thermodynamic parameters were denoted with negative values, demonstrating the spontaneous exothermic nature of the most favorable complexes. New energy states were observed within the extracted density of states plots, confirming the impact of adsorbing MeOH and EtOH molecules on the electronic properties of the Al12P12 nanocage. The appearance of additional peaks in Infrared Radiation (IR) and Raman spectra revealed the apparent effect of the adsorption process on the features of the utilized sensor. The emerging results declared the potential uses of Al12P12 nanocage as a promising candidate for sensing VOCs, particularly MeOH and EtOH.

Microhydration of small protonated polyaromatic hydrocarbons: a first principles study.

Using first principles methodology, we investigate the microsolvation of protonated benzene (BzH+), protonated coronene (CorH+) and protonated dodecabenzocoronene (DbcH+). Gas phase complexes of these small protonated polyaromatic hydrocarbons (H+PAHs) with mono-, di-, and tri-hydrated water molecules are considered. Their most stable forms are presented, where we discuss their structural, energetic aromaticity and IR and UV spectral features. In particular, we focus on the analysis of the bonding and various non-bonded interactions between these protonated aromatics and water clusters. The strength of non-bonded interactions is quantified and correlated with their electron density profiles. Furthermore, insights into the interfacial interactions and stability of these complexes were obtained through non-covalent index and symmetry-adapted perturbation theory (SAPT0) analyses. We also discuss the effects of the extension of the π aromatic cloud on the water solvation of these protonated aromatics. In particular, we extended our predictions for the S0 → S1 and S0 → T1 wavelength transitions of micro hydrated H+PAHs to deduce those of these species solvated in aqueous solution. The present findings should be useful for understanding, at the microscopic level, the effects of water interacting with H+PAHs, which are relevant for organic chemistry, astrochemistry, atmospheric chemistry, combustion and materials science.

Insight into melting point differences of dinitroimidazoles and dinitropyrazoles from the perspective of intermolecular interactions.

Dinitroimidazole (DNI) and dinitropyrazole (DNP), along with their congeners, possess similar molecular structures but exhibit distinct melting points. To analyse and elucidate the fundamental reasons for property differences from the perspective of intermolecular interactions, we proposed a simplified approach named binding energy in clusters (BEC) in computing weak interactions within complex crystal systems. Based on the results of the symmetry-adapted perturbation theory (SAPT) calculations, an approximate estimation of the melting point range can be derived by taking into account the cumulative effect (energy of electrostatic, dispersion and induction terms) and repulsive effect (energy of exchange term) values. We have also proposed a formula for calculating the specific melting point, which indicates that stronger intermolecular interactions have a major impact on the melting point, while the distribution of weak interactions also affects the melting point. This work would provide an effective reference for molecular design and structure-performance analysis.

Binary conformers of a flexible, long-chain fluoroalcohol: dispersion controlled selectivity and relative abundances in a jet.

The complex conformational panorama of binary 4,4,4-trifluoro-1-butanol (TFB) aggregates was investigated using chirped-pulse Fourier transform microwave spectroscopy, aided by conformational searches using CREST (Conformer-Rotamer Ensemble Sampling Tool) and quantum chemistry calculations. From nearly 1500 initial dimer geometries, 16 most stable binary candidates were obtained within a relative energy window of ∼4 kJ mol-1. Rotational spectra of five binary conformers were experimentally observed in supersonic expansion and assigned. Interestingly, three out of the five observed binary conformers are composed solely of monomer conformers, which were not observed in their isolated gas phase forms in jet expansion. In addition, an observed dimer that is made exclusively of the most stable TFB monomer subunits does not correspond to the global minimum. The intricate kinetically and thermodynamically controlled dimer formation mechanisms are discussed, and a modified kinetic-thermodynamic model was developed, providing conformational abundances that are in good agreement with the experiment. Subsequent non-covalent interaction analyses reveal that the observed conformers are held together by one primary O-H⋯O hydrogen bond and secondary intermolecular C-H⋯O, C-H⋯F, and/or O-H⋯F interactions, as well as C-H⋯H-C London dispersion interactions between the methylene groups. Further symmetry-adapted perturbation theory analyses of the TFB dimer conformers and related alcohol dimers reveal a considerable rise in dispersion contributions with increasing n-alkyl carbon chain length and highlight the role of dispersion interactions in preferentially stabilizing the global minimum of the TFB dimer.

R-8 Dispersion Interaction: Derivation and Application to the Effective Fragment Potential Method.

The anisotropic and isotropic R-8 dispersion contributions (disp8) are derived and implemented within the framework of the effective fragment potential (EFP) method formulated with imaginary frequency-dependent Cartesian polarizability tensors distributed at the centroids of the localized molecular orbitals (LMOs). Two forms of damping functions, intermolecular overlap-based and Tang-Toennies, are extended for disp8. To obtain LMO polarizability tensors centered at LMO centroids, an origin-shifting transformation is derived and implemented for the dipole-octopole polarizability tensor and the quadrupole-quadrupole polarizability tensor. The analytic gradient is derived and implemented for the isotropic disp8 contribution. Relative to the previously implemented empirical EFP disp8 energy, the isotropic disp8 component of the interaction energy improves the overall agreement of the EFP dispersion energies with the symmetry-adapted perturbation theory (SAPT) benchmarks, reducing the mean absolute errors (MAEs) and mean absolute percentage errors for most of the databases examined in this work. While the anisotropic disp8 can further enhance the accuracy of the EFP dispersion energy and yield smaller MAEs, significantly overbound dispersion energies are predicted by the anisotropic disp8 when the maximum element in the intermolecular overlap matrix is greater than 0.1, possibly due to the breakdown of the approximations made in the EFP dispersion derivation at a short range. For potential energy scan databases, the newly developed EFP dispersion model with isotropic disp8 yields the overall correct curvature and good agreement with SAPT benchmarks around equilibrium and longer but overestimates the dispersion interactions at a short range. While the overlap-based dispersion-damping functions produce better MAEs than Tang-Toennies damping functions, further improvement is needed to better screen the large attractive dispersion energies at a short range (overlap >0.1).