Interaction Potential Energy Surface Research Articles

High-Dimensional Atomistic Neural Network Potentials for Molecule-Surface Interactions: HCl Scattering from Au(111).

Ab initio molecular dynamics (AIMD) simulations of molecule-surface scattering allow first-principles characterization of the dynamics. However, the large number of density functional theory calculations along the trajectories is very costly, limiting simulations of long-time events and giving rise to poor statistics. To avoid this computational bottleneck, we report here the development of a high-dimensional molecule-surface interaction potential energy surface (PES) with movable surface atoms, using a machine learning approach. With 60 degrees of freedom, this PES allows energy transfer between the energetic impinging molecule and thermal surface atoms. Classical trajectory calculations for the scattering of DCl from Au(111) on this PES are found to agree well with AIMD simulations, with ∼105-fold acceleration. Scattering of HCl from Au(111) is further investigated and compared with available experimental results.

Stability of Van der Waals complexes of the greenhouse effect gases CH4 and SF6 with imidazole in gas mixtures containing CO2

Electronic structure calculations are applied to the study of the properties of the Zeolite Imidazolate Frameworks (ZIFs) for gas capture of the greenhouse effect gases CO2, CH4 and SF6. Van-der-Walls complexes of these adsorbates with imidazole are explored considering the imidazolate rings simplest models for the study of the nature of host-guest interactions in ZIFs. The minimum energy paths for complexation are described by determining global interaction potential energy surfaces. The approach of SF6 to the imidazole can produce its decomposition due to heterogeneous catalysis. The number of the complex stable geometries, depending on the size and polarity of the adsorbate, makes more probable its adsorption. The calculations prove that capture by imidazoles is energetically favored for the three adsorbates, CO2 displays the largest ability for binding imidazolate rings and methane presents the larger number of structures. CH4 and SF6 can be expected to be strong competitors while the molecular size of SF6 can yield to important steric effects. The stability of three body complexes type CH4-imidazole-CO2 and SF6-imidazole-CO2 confirms the probability of simultaneous attachments.

The first potential energy surfaces for the C6H(-)-H2 and C6H(-)-He collisional systems and their corresponding inelastic cross sections.

Molecular anions have recently been detected in the interstellar and circumstellar media. Accurate modeling of their abundance requires calculations of collisional data with the most abundant species that are usually He atoms and H2 molecules. In this paper, we focus on the collisional excitation of the first observed molecular anion, C6H(-), by He and H2. Theoretical calculations of collisional cross sections rely generally on ab initio interaction potential energy surfaces (PESs). Hence, we present here the first PESs for the C6H(-)-H2 and C6H(-)-He van der Waals systems. The ab initio energy data for the surfaces were computed at the explicitly correlated coupled cluster with single, double, and scaled perturbative triple excitations level of theory. The method of interpolating moving least squares was used to construct 4D and 2D analytical PESs from these data. Both surfaces are characterized by deep wells and large anisotropies. Analytical models of the PESs were used in scattering calculations to obtain cross sections for low-lying rotational transitions. As could have been anticipated, important differences exist between the He and H2 cross sections. Conversely, no significant differences exist between the collisions of C6H(-) with the two species of H2 (para- and ortho-H2). We expect that these new data will help in accurately determining the abundance of the C6H(-) anions in space.

Noncovalent Interactions and Impact of Charge Penetration Effects in Linear Oligoacene Dimers and Single Crystals

Noncovalent interactions determine in large part the thermodynamic aspects of molecular packing in organic crystals. Using a combination of symmetry-adapted perturbation theory (SAPT) and classical multipole electrostatics, we describe the interaction potential energy surfaces for dimers of the oligoacene family, from benzene to hexacene, including up to 5000 configurations for each system. An analysis of these surfaces and a thorough assessment of dimers extracted from the reported crystal structures underline that high-order interactions (i.e., three-body nonadditive interactions) must be considered in order to rationalize the details of the crystal structures. A comparison of the SAPT electrostatic energy with the multipole interaction energy demonstrates the importance of the contribution of charge penetration, which is shown to account for up to 50% of the total interaction energy in dimers extracted from the experimental single crystals; in the case of the most stable cofacial model dimers, this con...

A Refined Intermolecular Interaction Potential for Methane: Spectral Analysis and Molecular Dynamics Simulations

AbstractThe previously constructed methane interaction potential energy surface calculated at the second‐order Møller‐Plesset (MP2) perturbation theory has been significantly improved in two aspects. First, all ab initio potential energy data are calculated by the supermolecule counterpoise corrected coupled cluster with single and double and perturbative triple excitations [CCSD(T)] method with Dunning’s correlation‐consistent aug‐cc‐pVXZ, X=D, T, Q, 5, basis sets and extrapolated to the complete basis set (CBS) limits with a convergence precision of 0.01 kcal/mol. Second, instead of the simple 4‐site model proposed in the previous study, a 5‐site model has been used to represent the ab initio potential data. The simulated infrared spectrum using the potential energy surface seems to be broadly in line with the spectral features observed in experiments. Molecular dynamics simulations using the ab initio force field show quantitative agreements with experiments. The properties examined in this paper include the atom‐to‐atom radial distribution functions in liquid and supercritical phases and the self‐diffusion coefficients over a wide range of thermodynamic conditions. It is shown that the refined ab initio force field can be applied to study fluid properties in different phases.

Electron-Hole Pair Effects in Polyatomic Dissociative Chemisorption: Water on Ni(111).

The influence of electron-hole pairs in dissociative chemisorption of a polyatomic molecule (water) on metal surfaces is assessed for the first time using a friction approach. The atomic local density dependent friction coefficients computed based on a free electron gas embedding model are employed in classical molecular dynamics simulations of the water dissociation dynamics on rigid Ni(111) using a recently developed nine dimensional interaction potential energy surface for the system. The results indicate that nonadiabatic effects are relatively small and they do not qualitatively alter the mode specificity in the dissociation.

Accuracy of Quantum Mechanically Derived Force-Fields Parameterized from Dispersion-Corrected DFT Data: The Benzene Dimer as a Prototype for Aromatic Interactions.

A multilevel approach is presented to assess the ability of several popular dispersion corrected density functionals (M06-2X, CAM-B3LYP-D3, BLYP-D3, and B3LYP-D3) to reliably describe two-body interaction potential energy surfaces (IPESs). To this end, the automated Picky procedure ( Cacelli et al. J. Comput. Chem. 2012 , 33 , 1055 ) was exploited, which consists in parametrizing specific intermolecular force fields through an iterative approach, based on the comparison with quantum mechanical data. For each of the tested functionals, the resulting force field was employed in classical Monte Carlo and Molecular Dynamics simulations, performed on systems of up to 1000 molecules in ambient conditions, to calculate a number of condensed phase properties. The comparison of the resulting structural and dynamic properties with experimental data allows us to assess the quality of each IPES and, consequently, even the quality of the DFT functionals. The methodology is tested on the benzene dimer, commonly used as a benchmark molecule, a prototype of aromatic interactions. The best results were obtained with the CAM-B3LYP-D3 functional. Besides assessing the reliability of DFT functionals in describing aromatic IPESs, this work provides a further step toward a robust protocol for the derivation of sound force field parameters from quantum mechanical data. This method can be relevant in all those cases where standard force fields fail in giving accurate predictions.

Rotationally inelastic collisions of fulminic acid (HCNO) by He atom at low temperature

Rotational excitation cross sections and rate coefficients for the inelastic collision of HCNO by He atom are computed at low temperature. To perform this, an interaction potential energy surface of the HCNO(X1Σ+)–He(1S) van der Waals complex is obtained at the CCSD(T)/aug-cc-pVQZ level of theory. This potential presents a well depth of about 64.14cm−1 below the HCNO–He dissociation limit. The cross sections are obtained in the close coupling scheme and rate coefficients inferred by averaging the cross sections over a Maxwell–Boltzmann velocity distribution. A propensity towards ΔJ=1 transitions is observed.

Collisional quenching of highly rotationally excited HF

Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H$_2$ colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to $j=20$ were performed for kinetic energies from 10$^{-5}$ to 15000 cm$^{-1}$. State-to-state rate coefficients for temperatures between 0.1 and 3000 K are also presented. The comparison of the present results with previous work for lowly-excited rotational levels reveals significant differences. In estimating HF-H$_2$ rate coefficients, the reduced-potential method is found to be more reliable than the standard reduced-mass approach. The current state-to-state rate coefficient calculations are the most comprehensive to date for HF-He collisions. We attribute the differences between previously reported and our results to differences in the adopted interaction potential energy surfaces. The new He rate coefficients can be used in a variety of applications. The estimated H$_2$ and H collision rates can also augment the smaller datasets previously developed for H$_2$ and electrons.

Ground state analytical ab initio intermolecular potential for the Cl(2)-water system.

The chlorine/water interface is of crucial importance in the context of atmospheric chemistry. Modeling the structure and dynamics at this interface requires an accurate description of the interaction potential energy surfaces. We propose here an analytical intermolecular potential that reproduces the interaction between the Cl2 molecule and a water molecule. Our functional form is fitted to a set of high level ab initio data using the coupled-cluster single double (triple)/aug-cc-p-VTZ level of electronic structure theory for the Cl2 - H2O complex. The potential fitted to reproduce the three minima structures of 1:1 complex is validated by the comparison of ab initio results of Cl2 interacting with an increasing number of water molecules. Finally, the model potential is used to study the physisorption of Cl2 on a perfectly ordered hexagonal ice slab. The calculated adsorption energy, in the range 0.27 eV, shows a good agreement with previous experimental results.

On the use of explicitly correlated treatment methods for the generation of accurate polyatomic -He/H2 interaction potential energy surfaces: The case of C3-He complex and generalization.

Through the study of the C3(X1Σg (+)) (1)Σg (+)) + He((1)S) astrophysical relevant system using standard (CCSD(T)) and explicitly correlated (CCSD(T)-F12) coupled cluster approaches, we show that the CCSD(T)-F12/aug-cc-pVTZ level represents a good compromise between accuracy and low computational cost for the generation of multi-dimensional potential energy surfaces (PESs) over both intra- and inter-monomer degrees of freedom. Indeed, the CCSD(T)-F12/aug-cc-pVTZ 2D-PES for linear C3 and the CCSD(T)-F12/aug-cc-pVTZ 4D-PES for bent C3 configurations gently approach those mapped at the CCSD(T)/aug-cc-pVXZ (X = T,Q) + bond functions level, whereas a strong reduction of computational effort is observed. After exact dynamical computations, the pattern of the rovibrational levels of the intermediate C3-He complex and the rotational and rovibrational (de-) excitation of C3 by He derived using both sets of PESs agree quite well. Since C3 shows a floppy character, the interaction PES is defined in four dimensions to obtain realistic collisional parameters. The C-C-C bending mode, which fundamental lies at 63 cm(-1) and can be excited at very low temperatures is explicitly considered as independent coordinate. Our work suggests hence that CCSD(T)-F12/aug-cc-pVTZ methodology is the key method for the generation of accurate polyatomic - He/H2 multi-dimensional PESs.

Dispersion interactions in small zinc, cadmium, and mercury clusters.

Dispersion interactions in small clusters of group XII (Zn, Cd, Hg) metal atoms are studied at the CCSD(T) level with triple-ζ basis sets. A pair potential model together with a least-squares fit to the interaction potential energy surface is used to calculate interatomic dispersion coefficients, which are found to be in good agreement with atomistic calculations. The angular dependence of the dispersion interaction, extracted by explicitly accounting for the leading order electrostatic and induction terms, is determined with the aid of a coupled spherical harmonic expansion. The distance dependence of the orientation averaged dispersion energy is modeled by an integral average of our potential model, which is able to robustly account for the average dispersion energy to a remarkable degree.

ON THE VALIDITY OF COLLIDER-MASS SCALING FOR MOLECULAR ROTATIONAL EXCITATION

Rate coefficients for collisional processes such as rotational and vibrational excitation are essential inputs in many astrophysical models. When rate coefficients are unknown, they are often estimated using known values from other systems. The most common example is to use He-collider rate coefficients to estimate values for other colliders, typically H$_2$, using scaling arguments based on the reduced mass of the collision system. This procedure is often justified by the assumption that the inelastic cross section is independent of the collider. Here we explore the validity of this approach focusing on rotational inelastic transitions for collisions of H, para-H$_2$, $^3$He, and $^4$He with CO in its vibrational ground state. We compare rate coefficients obtained via explicit calculations to those deduced by standard reduced-mass scaling. Not surprisingly, inelastic cross sections and rate coefficients are found to depend sensitively on both the reduced mass and the interaction potential energy surface. We demonstrate that standard reduced-mass scaling is not valid on physical and mathematical grounds, and as a consequence, the common approach of multiplying a rate coefficient for a molecule-He collision system by the constant factor of ~1.4 to estimate the rate coefficient for para-H$_2$ collisions is deemed unreliable. Furthermore, we test an alternative analytic scaling approach based on the strength of the interaction potential and the reduced mass of the collision systems. Any scaling approach, however, may be problematic when low-energy resonances are present; explicit calculations or measurements of rate coefficients are to be preferred.

The excited-states intermolecular potential energy surfaces of the Ar–CS2 van der Waals complex: Ab initio study

The sixteen lowest potential energy surfaces (PESs) of the electronically excited Ar–CS2 van der Waals (vdW) complex are calculated in the singlet state. PESs are obtained based on the vertical excitation of the complex containing the linear geometry ground electronic state (1Σg+) of CS2 molecule to the valence excited electronic states. The computational method involves EOM-CCSD with the aug-cc-pVDZ basis set augmented with a set of midbond functions (3s3p2d1f1g). It was found that some forbidden electronic transitions like 1Σg+→1Πg in the CS2 monomer become possible due to the presence of the Ar atom. The interaction PESs with the visible well-depth for all of the configurations are globally fitted to an analytic function in order to estimate the isotropic dipole–dipole (C60) and dipole–quadrupole (C80) coefficients of the excited states of the complex.

Aggregated ion pairs of [MIM+][N(CN)2−]2 ionic liquid: A quantum chemical study in solvents with different dielectric constants

The aggregated ion pairs of [MIM+][N(CN)2−] ionic liquid have been studied using MP2, B3LYP, M05-2X and M06-2X methods in conjunction with the 6-311++G(2d,2p) basis set. Five aggregated ion pairs (2-IP1-5) were characterized on the potential energy surface of interaction of two cations with two anions. The geometrical parameters, Gibbs free energy of formation in gas and solution phases (ΔG° and ΔGsln°) and solvation Gibbs free energy were calculated for aggregates of [MIM+][N(CN)2−]. The range of ΔG° was 3.3 to −10.4kcal/mol at MP2/6-311++G(2d,2p) level of theory. The ΔG° value first significantly decreases with increasing solvent dielectric constant and then changes smoothly when the dielectric constant becomes greater than 20.0. The results of the temperature dependence of ΔG° revealed that the tendency for aggregation decreases as the temperature increases. Frequency analysis showed a significant red-shift in the N–H stretching vibrational wave number of 2-IP1 and 2-IP2 aggregates. Population analysis shows that the charge transfer (CT) taking place from anion N(CN)2− to cation MIM+ upon complex formation.

QUENCHING OF HIGHLY ROTATIONALLY EXCITED HCl IN COLLISIONS WITH He

We report rotational quenching cross sections and rate coefficients of HCl due to collisions with He. The close-coupling method and the coupled-states approximation are applied in quantum-mechanical scattering calculations of state-to-state cross sections for HCl with initial rotational levels up to $j=20$ for kinetic energies from 10$^{-5}$ to 15000 cm$^{-1}$. State-to-state rate coefficients for temperature between 0.1 and 3000 K are also presented. Comparison of the present rate coefficients with previous results reported in the literature for lowly-excited rotational levels shows reasonable agreement. Small differences are attributed to the differences in the interaction potential energy surfaces. The uncertainty in the computed cross sections and rate coefficients is estimated by varying the potential well depth. Applications of current results to astrophysical systems are also briefly discussed.

Vibrational Shifts of HXeCl in Matrix Environments

The hybrid quantum-classical simulations are performed to investigate the unusual vibrational spectral shifts of a noble-gas hydride HXeCl in matrix environments (in Ne, Ar, Kr, and Xe matrixes). The high-level ab initio calculations at the CCSD(T) level are employed to construct interaction potential energy surfaces between HXeCl and noble-gas atoms (Ne, Ar, Kr, and Xe). The configurations of noble-gas atoms are sampled by the Monte Carlo simulations and the vibrational levels of HXeCl in the presence of the surrounding noble-gas atoms are solved by the DVR approach. It is found that the H-Xe stretching frequencies are blue-shifted from the isolated gas-phase value in all matrix environments and that the relative blue shifts are in good agreement with the experimental results (Ne < Xe < Kr), demonstrating that the explicit treatment of matrix environments around HXeCl is essential to reproduce the observed unusual vibrational shifts.

Theoretical study on molecular packing and electronic structure of bi-1,3,4-oxadiazole derivatives

One of the energy-minimum structures predicted by the intermolecular interaction potential energy surface computed using the M062x/6-31G** method closely resembled the crystal packing.

Comparison of multireference configuration interaction potential energy surfaces for H + O2 → HO2: the effect of internal contraction

A comparison is presented of uncontracted multireference singles and doubles configuration interaction (MRCI) and internally contracted MRCI potential energy surfaces for the reaction \( {\mathrm H}\left( {^2 {\mathrm S}} \right) + {\mathrm O}_2 \left( {^3 \Sigma _{g}^ - } \right) \to {\mathrm H}{\mathrm O}_2 \left( {^2 {\mathrm A}^{\prime\prime}} \right) \). It is found that internal contraction leads to significant differences in the reaction kinetics relative to the uncontracted calculations.

Rotational excitation of protonated hydrogen cyanide (HCNH+) by He atom at low temperature

We report on ab initio coupled-cluster calculations of the interaction potential energy surface for the HCNH+–He complex. The aug-cc-pVTZ Gaussian basis, to which is added a set of bond functions placed at mid-distance between HCNH+ center of mass and He atom is used. The HCNH+ bonds length are set to their values at the equilibrium geometry, i.e., r e [HC]=1.0780 A, r e [CN]=1.1339 A and r e [NH]=1.0126 A. The interaction energy presents a global minimum located $266.9~\mathrm{cm^{-1}}$ below the HCNH+–He dissociation limit. Using the interaction potential obtained, we have computed rotational excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature (T≤120 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments.