Extended Basis Sets Research Articles

Structures, energies, and bonding in the microsolvation of Na+

A stochastic search of the potential energy surfaces for the interctions between the sodium cation and up to six explicit water molecules was performed under Møller–Plesset second–order perturbation theory (MP2) with extended basis sets. At these low molecularties, the sodium cation is more likely to occupy the interior of the cluster, energetically favoring a maximum coordination number of four, even when five or six water molecules are available. An energy decomposition analysis reveals a major contribution from electrostatic interactions to cluster stabilization, with non-negligigle induction contributions accounting for ≈20% of the total interaction. Topological analysis of the electron distribution unambiguously describe H2O⋯Na+ ionic interactions. Hydrogen bond networks seem to arrange in order to maximize the stability of Na+ via a clear charge transfer pattern, where electron density is withdrawn from the O–H bonds towards Na+. Because of this reorganization of the electron density, and because of the perturbative effect of the formal charge, all H2O⋯H2O hydrogen bonds are also highly ionic in nature with some degree of covalency.

Structural, spectroscopic, electronic, and nonlinear optical behavior investigations of  conjugated organic nonlinear optical chalcone derivative 3-(2,3-dichlorophenyl)-1-(pyridine-2-yl)prop-2-en-1-one using DFT

In this paper we have reported the computational studies of structural, spectroscopic and electronic behavior of a chalcone derivative: 3-(2,3- dichlorophenyl )-1-(pyridine-2- yl)prop-2-en-1-one (DCPP) nonlinear optical crystal. The geometry of DCPP molecule have been optimized using density functional theory (DFT) at B3LYP level having extended basis sets 6-311++G(d,p), 6-311+G(d,p), and 6-311G(d,p) with the help of Gaussian 09W program package. The structure parameters calculated with 6-311++G(d,p) basis set have shown best matching with experimental data having R 2 value equal to 0.99. Taking this optimized geometry FTIR spectra were simulated and analyzed quantitatively with the help of calculated potential energy distribution (PED). For finding the reactivity sites and to understand electronic and optical behavior, natural bond orbital (NBO), the electrostatic potential surface map with isodensity surface, and HOMO-LUMO analysis were also presented. Finally, the nonlinear optical behavior of this calcone derivative was studied by calculating dipole moment (m), polarizability(a) and hyperpolarizability (b) values. The calculated hyperpolarizability b tot of DCPP is 17.4593×10 -30 esu which is about 90 times greater than urea (β= 0.1947× 10-30 esu). This higher value of hyperpolarizability b tot confirms that the present molecule DCPP is a potential candidate for Nonlinear Optical applications.

Smart local orbitals for efficient calculations within density functional theory and beyond.

Localized basis sets in the projector augmented wave formalism allow for computationally efficient calculations within density functional theory (DFT). However, achieving high numerical accuracy requires an extensive basis set, which also poses a fundamental problem for the interpretation of the results. We present a way to obtain a reduced basis set of atomic orbitals through the subdiagonalization of each atomic block of the Hamiltonian. The resulting local orbitals (LOs) inherit the information of the local crystal field. In the LO basis, it becomes apparent that the Hamiltonian is nearly block-diagonal, and we demonstrate that it is possible to keep only a subset of relevant LOs that provide an accurate description of the physics around the Fermi level. This reduces to some extent the redundancy of the original basis set, and at the same time, it allows one to perform post-processing of DFT calculations, ranging from the interpretation of electron transport to extracting effective tight-binding Hamiltonians, very efficiently and without sacrificing the accuracy of the results.

In Ukrainian

Studying interaction of zinc (II) with silica and alumina-silica surfaces is important for several reasons. From a practical point of view, it is carried out in the framework of the creation of a medicinal product, the ingredients of which are, in particular, silica(alumina)containing sorbent and zinc compound; from a theoretical point of view, it is a search for the adsorption patterns on the mentioned surfaces in a series of d-elements with a close electronic structure (zinc, copper, nickel, cadmium, etc.). In addition, it is advisable to supplement the experimental adsorption data with the results of quantum chemical simulation of the structure and formation energy of zinc (II) complexes with active surface centers. Adsorption of Zn 2+ ions from a neutral aqueous solution on silica and alumina-silica materials was studied by means of the method of adsorption isotherm. The specific surface of the materials was determined by method of thermal desorption of argon. Quantum chemical analysis of the structure and energy of formation of the hydrated zinc sulfate ion pair on silica and alumina-silica surfaces was performed by means of Hartree-Fock-Roothaan method with extended basis set 6‑31++G(d,p). According to the magnitude of adsorption (A) of zinc, the test materials are divided into three groups: 1) enterosgel, kaolin, nanosilica A-300 and polymethylsiloxane, for which А max is from 0.15 to 0.3 mg/g; 2) Syloid® 244 FP, KG-60 and KG-40, aminopropylaerosil, smectite (А max from 1.2 to 12.0 mg/g); 3) zeolites NaA-TK-1173 and NaX (А max more than 30 mg/g). It is concluded that the high adsorption activity of zinc(II) is primarily due to the presence of developed porous structure. The most probable places of interaction between hydrated zinc ions and hydroxyl group of silica and alumina-silica surfaces are determined by means of quantum chemical simulation. The pK Me values have been calculated of ion exchange of silica surface when interacting with Zn 2+ cations.

Temozolomide binding to Cucurbit[7]uril: QTAIM, NCI-RDG and NBO analyses

The inclusion behavior of antineoplastic Temozolomide (TMZ) in the cavitand host Cucurbit[7]uril (CB[7]), with 1:1 stoichiometry, was investigated in this research work. Structural and electronic studies were conducted in vacuum and water. We used the DFT/B3LYP and the dispersion corrected DFT-D/wB97X-D functionals with 6-31G(d), 6–31 + G(d) and 6-31 + G(d,p) basis sets. All methods agree on the 3D optimum structure, in which a total inclusion of TMZ in CB[7] cavity is observed. A destabilizing effect of solvation was highlighted and confirmed from Frontier Molecular Orbital and global reactivity descriptors analyses. Furthermore, The nature and strength of intermolecular interactions were studied using Natural Bond Orbital (NBO) and Quantum Theory of Atoms In Molecule (QTAIM) analyses. Both models corroborate on the overall conclusion revealing that the conventional N–H⋯O and improper C–H⋯O H-bonds are mainly the driving forces stabilizing TMZ@CB[7] complex. Also, in the framework of the topological QTAIM analysis, we classified these closed shell interactions and distinguished two kinds of H-bonds: with electrostatic character or partially covalent in nature. The analysis of Espinosa energies unveils a good correlation with the intermolecular bond distance and electron density. Moreover, The Non-Covalent Interactions Reduced Density Gradient (NCI-RDG) method was used to reveal and distinguish between weak interaction regions; in fact it segregates attractive (H-bonding), dispersive (VdW) and repulsive interactions. Finally, from 1H NMR and TD-DFT computations, we identified, the interaction sites and the electronic transitions responsible of UV–Vis absorption bands, respectively. The best reproduction of experimental spectra is achieved with the dispersion corrected wB97X-D and extended basis sets.

Solubility of sulfanilamide in binary solvents containing water: Measurements and prediction using Buchowski-Ksiazczak solubility model

The solubility of Sulfanilamide in binary mixtures comprising water and five organic solvents was studied at different temperatures using a spectrophotometric method. Additionally, the differential scanning calorimetry (DSC) measurements were performed to characterize the non-dissolved portion of Sulfanilamide obtained after shake-flask experiments. The Buchowski-Ksiazczak solubility model was applied to interpret the obtained experimental results. The model was successful in reproducing experimental data, as it was evidenced by several statistical measures, including the Akaike Information Criterion. The obtained parameters of the λh-equation were used for calculating the values of enthalpy of mixing. It was observed that the minimum value of enthalpy of mixing for each system is associated with those binary solvent compositions which result in the highest solubility of Sulfanilamide. Also the maximum value of the λ parameter corresponds to the composition of the mixture yielding the highest solubility. The application of COSMO-RS methodology revealed the sensitivity of solute activities and solvation Gibbs free energies to solvent-cosolvent composition. Also, there was noticed a strong correlation of these thermodynamic properties. It happened that low values of Sulfanilamide activities and their monotonous variations with the composition of considered binary solutions are associated with monotonous solubility profiles and also the reverse conclusion holds. Besides, differences in solvation of monomers and intermolecular complexes are the very probable origins of the observed trends in excess enthalpies of saturated solutions. The advanced quantum chemistry computations, including electron correlation and extended basis set, were used for quantification of affinities of systems components toward pairs formation. From the obtained values of activity equilibrium constants it was concluded that the highest affinity in all studied conditions should be attributed to Sulfanilamide dimers. It was also observed that pairs formed by Sulfanilamide with water are more thermodynamically stable than the ones with cosolvent molecules with only one exception, namely 1,4-dioxane.

On the basis set selection for calculations of core-level states: different strategies to balance cost and accuracy

We present a study on basis set effects in correlated calculations of core-level states. While it is well recognised that the core-level states require using more extensive basis sets than their valence counterparts, the standard strategy has been to use large contracted basis sets, such as the cc-pVXZ or cc-pCVXZ series. Building upon the ideas of Besley et al. [J. Chem. Phys. 130, 124308 (2009)], we show that a much more effective strategy is to use uncontracted bases, such as core or fully uncontracted Pople's basis. The physical grounds behind this approach are explained and illustrated by numeric results. We also discuss other cost-saving strategies, such as virtual space truncation and mixed precision execution.

PSIXAS: A Psi4 plugin for efficient simulations of X-ray absorption spectra based on the transition-potential and Δ-Kohn-Sham method.

Near edge X-ray absorption fine structure (NEXAFS) spectra and their pump-probe extension (PP-NEXAFS) offer insights into valence- and core-excited states. We present PSIXAS, a recent implementation for simulating NEXAFS and PP-NEXAFS spectra by means of the transition-potential and the Δ-Kohn-Sham method. The approach is implemented in form of a software plugin for the Psi4 code, which provides access to a wide selection of basis sets as well as density functionals. We briefly outline the theoretical foundation and the key aspects of the plugin. Then, we use the plugin to simulate PP-NEXAFS spectra of thymine, a system already investigated by others and us. It is found that larger, extended basis sets are needed to obtain more accurate absolute resonance positions. We further demonstrate that, in contrast to ordinary NEXAFS simulations, where the choice of the density functional plays a minor role for the shape of the spectrum, for PP-NEXAFS simulations the choice of the density functional is important. Especially hybrid functionals (which could not be used straightforwardly before to simulate PP-NEXAFS spectra) and their amount of "Hartree-Fock like" exact exchange affects relative resonance positions in the spectrum.

Hybrid-functional electronic structure of multilayer graphene

Multilayer graphene with rhombohedral and Bernal stacking are supposed to be metallic, as predicted by density functional theory calculations using semi-local functionals. However recent angular resolved photoemission and transport data have questioned this point of view. In particular, rhombohedral flakes are suggested to be magnetic insulators. Bernal flakes composed of an even number of layers are insulating, while those composed of an odd number of layers are pseudogapped. Here, by systematically benchmarking with plane waves codes, we develop very accurate all-electron Gaussian basis sets for graphene multilayers. We find that, in agreement with our previous calculations, rhombohedral stacked multilayer graphene are gapped for and magnetic. However, the valence band curvature and the details of the electronic structure depend crucially on the basis set. Only substantially extended basis sets are able to correctly reproduce the effective mass of the valence band top at the K point, while the popular POB-TZVP basis set leads to a severe overestimation. In the case of Bernal stacking, we show that exact exchange gaps the flakes composed by four layers and opens pseudogaps for N = 3, 6, 7, 8. However, the gap or pseudogap size and its behaviour as a function of thickness are not compatible with experimental data. Moreover, hybrid functionals lead to a metallic solution for 5 layers and a magnetic ground state for 5, 6 and 8 layers. Magnetism is very weak with practically no effect on the electronic structure and the magnetic moments are mostly concentrated in the central layers. Our hybrid functional calculations on trilayer Bernal graphene multilayers are in excellent agreement with non-magnetic GW calculations. For thicker multilayers, our calculations are a benchmark for manybody theoretical modeling of the low energy electronic structure.

Stability of the negative ion of hydrogen in nonideal classical plasmas.

The stability of the negative ion of hydrogen (H^{-}) embedded in nonideal classical plasma has been studied by computing the ground state energy of the ion quite accurately. The interactions among the charged particles in plasma have been modelled by a pseudopotential, derived from a solution of Bogolyubov's hierarchy equations. An extensive basis set is employed in Rayleigh-Ritz variational method to compute the ground state energy of H^{-} for various values of plasma parameters. Effects of nonideality of plasma on the stability of the ion have been investigated in detail for a wide range of nonideality. Particular emphasis is made to compute accurately the critical values of the plasma screening parameters.

Detailed Pair Natural Orbital-Based Coupled Cluster Studies of Spin Crossover Energetics.

In this work, a detailed study of spin-state splittings in three spin crossover model compounds with DLPNO-CCSD(T) is presented. The performance in comparison to canonical CCSD(T) is assessed in detail. It was found that spin-state splittings with chemical accuracy, compared to the canonical results, are achieved when the full iterative triples (T1) scheme and TightPNO settings are applied and relativistic effects are taken into account. Having established the level of accuracy that can be reached relative to the canonical results, we have undertaken a detailed basis set study in the second part of the study. The slow convergence of the results of correlated calculations with respect to basis set extension is particularly acute for spin-state splittings for reasons discussed in detail in this Article. In fact, for some of the studied systems, 5Z basis sets are necessary in order to come close to the basis set limit that is estimated here by basis set extrapolation. Finally, the results of the present work are compared to available literature. In general, acceptable agreement with previous CCSD(T) results is found, although notable deviations stemming from differences in methodology and basis sets are noted. It is noted that the published CASPT2 numbers are far away from the extrapolated CCSD(T) numbers. In addition, dynamic quantum Monte Carlo results differ by several tens of kcal/mol from the CCSD(T) numbers. A comparison to DFT results produced with a range of popular density functionals shows the expected scattering of results and showcases the difficulty of applying DFT to spin-state energies.

Electron Attachment to DNA Base Pairs: An Interplay of Dipole- and Valence-Bound States.

We have investigated the electron-attached states in Watson-Crick guanine-cytosine and adenine-thymine base pairs using the highly accurate equation-of-motion coupled-cluster (EOM-CC) method and extended basis sets. Both base pairs have two bound anionic states. The dipole-bound state is stable even at the neutral geometry, but the valence-bound state is only adiabatically bound. The initial electron attachment results in the formation of a dipole-bound state that acts as a doorway to the valence-bound anionic state. The adiabatic potential energy surface of ground and first excited states of an anion shows an avoided crossing, indicating mixing of the electronic and nuclear degrees of freedom. We have calculated the coupling strength between the valence- and dipole-bound states by fitting a simple diabatic model potential to a cut through the two adiabatic surfaces of the anions obtained from the EOM-CC calculations. The transfer of the electron from the initial dipole-bound to the final valence-bound state has been found to happen at an ultrafast time scale.

H2 adsorptions to CuRg (Rg = He-Kr) cation I and II series.

Structures and stabilities of H2 adsorption to CuRg (Rg = He-Kr) cation I and II series are performed at CCSD(T) theoretical level with extended basis sets. "T-shaped" structures of H2 adsorptions to Cu or Rg atoms with different dissociation energies can be found (H2-CuRgQ or H2-RgCuQ). Further calculations confirm the adsorptions of two H2 ligands (H2-CuKrQ-H2). The Rg = Kr series show enhanced stabilities and good dehydrogenation abilities, suggesting potential applications in hydrogen storage applications.

Infrared Signatures of the HHen+ and DHen+ (n = 3-6) Complexes.

Combination of a cryogenic ion-trap machine, operated at 4.7 K, with the free-electron-laser FELIX allows the first experimental characterization of the unusually bright antisymmetric stretch (ν3) and π-bending (ν2) fundamentals of the He-X+-He (X = H, D) chromophore of the in situ prepared HHen+ and DHen+ (n = 3-6) complexes. The band origins obtained are fully supported by first-principles quantum-chemical computations, performed at the MP2, the CCSD(T), and occasionally the CCSDTQ levels employing extended basis sets. Both the experiments and the computations are consistent with structures for the species with n = 3 and 6 being of T-shaped C2v and of D4h symmetry, respectively, while the species with n = 4 are suggested to exhibit interesting dynamical phenomena related to large-amplitude motions.

The Effects of Split Valence Basis Sets on Muon Hyperfine Interaction in Guanine Nucleobase and Nucleotide Structures

The DFT cluster method was employed to investigate the electronic structures and muonium hyperfine interactions in guanine nucleobase and nucleotide using three different basis sets. The total energy and Fermi contact values were calculated for muon trapped at carbon '8'. The three basis sets, 6-31G, 6-311G and 6-311G(d,p), were used in tandem with the B3LYP functional. There are significant quantitative differences in the calculated total energy. 6-311G(d,p) produced the lowest total energy as compared to the other basis sets. The lowering of the total energy is due to the increase in the number of basis functions to describe the atomic orbitals, which is consistent with the postulate on basis set completeness. The 6-31G basis set produced the muon Fermi contact value that is the closest to the experimental value. The calculated Fermi contact values for the nucleobase and nucleotide are significantly lowered in going from the double-zeta to the triple-zeta basis set by 5% and 4% respectively. The lowering of the Fermi contact value can be attributed to the extension of the triple-zeta basis set in describing the valence atomic orbitals. The presence of the sugar phosphate group in the nucleotide instead of the methyl group tends to lower the Fermi contact value. Thus, the sugar phosphate group should be taken into consideration when designing a calculation model.

Many-Body Expanded Full Configuration Interaction. II. Strongly Correlated Regime.

In this second part of our series on the recently proposed many-body expanded full configuration interaction (MBE-FCI) method, we introduce the concept of multideterminantal expansion references. Through theoretical arguments and numerical validations, the use of this class of starting points is shown to result in a focused compression of the MBE decomposition of the FCI energy, thus allowing chemical problems dominated by strong correlation to be addressed by the method. The general applicability and performance enhancements of MBE-FCI are verified for standard stress tests such as the bond dissociations in H2O, N2, C2, and a linear H10 chain. Furthermore, the benefits of employing a multideterminantal expansion reference in accelerating calculations of high accuracy are discussed, with an emphasis on calculations in extended basis sets. As an illustration of this latter quality of the MBE-FCI method, results for H2O and C2 in basis sets ranging from double- to pentuple-ζ quality are presented, demonstrating near-ideal parallel scaling on up to almost 25000 processing units.

Pyrrolidinium‐based ionic liquids as electrolytes for lithium batteries: A Computational Study

AbstractElectrochemical windows (ECWs) of the cyclic ammonium based ionic liquids formed by the combination of two common pyrrolidinium cations—N,N‐butylmethyl pyrrolidinum(Pyr14) and N,N‐hexylmethyl pyrrolidinium(Pyr16) and five anions—dicyanamide, trifluoroacetate, fluoromethane sulfonate, bis((trifluoromethylsulfonyl)imide, and bis(fluorosulfonyl)imide were investigated. The ECW of each ionic liquid was obtained from the oxidation and reduction potentials of these ionic liquids with respect to a Li+/Li reference electrode by using thermodynamic cycle method. The work reveals that the ECWs of these ionic liquids are solely decided by the HOMO energy of pairing anions. The ECWs were also computed using HOMO‐LUMO method employing Møller‐Plesset perturbation theory to the second order and M06L methods with a basis set of 6‐31 + G(d, p). The ECW computed using M06L functional with an extended basis set of 6‐311++G(d, p) showed better agreement with experimental values suggesting accurate computation of ECW is possible at lower computational cost.

On the interaction of propynal with HNO, HF, HCl, H2O, CH3OH, and NH3: Red- and blue-shifting hydrogen bonds and tetrel bonds

The potential energy surfaces of the complexes of propynal, (propiolaldehyde, propargyl aldehyde, HCCCOH), with a series of small molecules (HNO, HF, HCl, H2O, CH3OH, and NH3) have been investigated theoretically at the MP2 and CCSD(T) levels using several extended basis sets. Thirty low-lying minima have been detected, eight for HCCCOH-HNO, four for each of the dimers HCCCOH-HF, HCCCOH-HCl, and HCCCOH-H2O, seven for the HCCCOH-CH3OH complex, and three for HCCCOH-NH3. The most stable HCCCOH-HNO complex has a non-planar, orthogonal structure with a tetrel bond and a hydrogen bond. In most cases the calculated intramolecular bond length changes as induced by complex formation are allegeable on the basis of the intramolecular harmonic force fields of propynal and the partner molecules. The vibrational frequency shifts, typical for formyl groups engaged in hydrogen bonding, red shifts of CO stretches and blue shifts of CH stretches, occur in most of the dimers, whereas the acetylenic CH and CC stretches are red-shifted when this CH bond is involved in hydrogen bonding. In almost all HCCCOH-HNO complexes, the NH stretching frequency is also blue-shifted. However, in case of the most stable HCCCOH-HNO complex a red-shift of the harmonic NH stretch is calculated. Inclusion of anharmonic contributions reduces this red shift substantially and even converts it to a blue shift. Conventional red shifts of X-H (X = F, Cl, O) stretching frequencies and blue shifts for formyl CH stretches are calculated for most of the complexes with HF, HCl, H2O, CH3OH, and NH3.

Automatic basis-set adaptation in projection-based embedding.

Projection-based embedding (PbE) is an exact embedding method within density-functional theory (DFT) that has received increasing attention in recent years. Several different variants have been described in the literature, but no systematic comparison has been presented so far. The truncation of the basis is critical for the efficiency of this class of approaches. Here, we employ a basis-set truncation scheme previously used for level-shift embedding in a top-down fashion, and we present an own basis-set extension scheme for bottom-up type PbE. We compare its accuracy for the level-shift technique [Manby et al., J. Chem. Theory Comput. 8, 2564-2568 (2012)] and an empirically corrected variant, the external-orthogonality approach by Khait and Hoffmann [Annu. Rep. Comput. Chem. 8, 53-70 (2012)] and the approach based on the Huzinaga equation transferred to the DFT context [Hégely et al., J. Chem. Phys. 145, 064107 (2016)]. Concerning the reproduction in total energies, we show that the Huzinaga method yields the most stable results concerning a basis-set truncation in top-down embedding. For the practically more relevant calculation of energy differences, the efficient level-shift technique yields very promising results due to error cancellation. In bottom-up embedding, we observe convergence issues in cases where constraints in the Lagrange formalism cannot be fulfilled due to basis-set incompleteness.

First principles study of structural and optical properties of [formula omitted] isomers

In this work we undertake a comprehensive numerical study of the ground state structures and optical absorption spectra of isomers of B12 cluster. Geometry optimization was performed at the coupled-cluster-singles-doubles (CCSD) level of theory, employing cc-pVDZ extended basis sets. Once the geometry of a given isomer was optimized, its ground state energy was calculated more accurately at the coupled-cluster-singles-doubles along with perturbative treatment of triples (CCSD(T)) level of theory, employing larger cc-pVTZ basis sets. Thus, our computed values of binding energies of various isomers are expected to be quite accurate. Our geometry optimization reveals eleven distinct isomers, along with their point group, and electronic ground state symmetries. We also performed vibrational frequency analysis on the three lowest energy isomers, and found them to be stable. Therefore, we computed the linear optical absorption spectra of these isomers of B12, employing large-scale multi-reference singles-doubles configuration-interaction (MRSDCI) approach, and found a strong structure-property relationship. This implies that the spectral fingerprints of the geometries can be utilized for optical detection, and characterization, of various isomers of B12. We also explored the stability of the isomer with the structure of a perfect icosahedron, with Ih symmetry. In bulk boron icosahedron is the basic structural unit, but, our vibrational frequency analysis reveals that it is unstable in the isolated form. We speculate that this instability could be due to Jahn-Teller distortion because five-fold degenerate HOMO orbitals in Ih structure are unfilled.