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This study aims to cast light on the nature of hydrogen bonds and their cooperativity that exists in alcohol-water ( $ \textrm{ROH}{({{\textrm{H}_2}\textrm{O}})_\textrm{n}} $ ROH ( H 2 O ) n ) ( $ \textrm{R} = - \textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Me}}),\textrm{ } - \textrm{C}{\textrm{H}_2}\textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Et}}) $ 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 ( $ \textrm{ROH} $ ROH ) forms two hydrogen bonds, one primary hydrogen bond $ ({\textrm{O} - \textrm{H} \cdot \cdot \cdot \textrm{O}}) $ (O − H ⋅ ⋅ ⋅ O) , and one secondary hydrogen bond $ ({\textrm{C} - \textrm{H} \cdot \cdot \cdot \textrm{O}}) $ (C − H ⋅ ⋅ ⋅ O) Two types of hydrogen bonds are addressed in these studies, where alcohol works as the hydrogen bond donor $ ({\textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2}}) $ (ROH ⋅ ⋅ ⋅ O H 2 ) and hydrogen bond acceptor $ ({\textrm{RHO} \cdot \cdot \cdot \textrm{HOH}}) $ (RHO ⋅ ⋅ ⋅ HOH). The AIM results reveal that $ \textrm{RHO} \cdot \cdot \cdot \textrm{HOH} $ RHO ⋅ ⋅ ⋅ HOH and $ \textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2} $ 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 $ \textrm{ROH} \cdot \cdot \cdot \textrm{O}{\textrm{H}_2} $ ROH ⋅ ⋅ ⋅ O H 2 and $ \textrm{RHO} \cdot \cdot \cdot \textrm{HOH} $ RHO ⋅ ⋅ ⋅ HOH hydrogen bond, and cooperative effect in ( $ \textrm{ROH}{({{\textrm{H}_2}\textrm{O}})_\textrm{n}} $ ROH ( H 2 O ) n ) ( $ \textrm{R} = - \textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Me}}),\textrm{ } - \textrm{C}{\textrm{H}_2}\textrm{C}{\textrm{H}_3}\textrm{ }({ - \textrm{Et}}) $ R = − C H 3 (− Me) , − C H 2 C H 3 (− Et).) (n = 1–10). [ABSTRACT FROM AUTHOR]

A molecular crystal structure prediction (CSP) protocol used in the seventh blind test is presented. The seventh blind test was divided into two stages and included seven targets, with crystals containing from one to three molecules in asymmetric units, monomers built of up to 100 atoms, and all targets containing monomers with flexible degrees of freedom. Some targets were cocrystals and one target was a salt. These diverse targets were treated using a CSP protocol starting from finding the global and local minima conformations of the target molecule. Subsequently, an ab initio two‐body rigid‐monomer six‐dimensional force field (aiFF) was developed for the global‐minimum conformer. These aiFFs were then used in CSPs consisting of packing and lattice‐energy minimization stages. Flexible‐monomer CSPs were used for some targets. To describe the intramonomer FF, either generic empirical FFs or reparametrized FFs of this type were used, with some parameters fitted to ab initio energies of monomers in the latter case. A novel packing procedure was applied for two targets in stage 1. The success rate in the structure generation stage was 15% in submission phase and 54% in post‐submission phase, while the corresponding values in the structure rating stage were 33% and 89%. We conclude that the inexpensive conformer‐based approach with rigid‐monomer CSPs can be recommended for investigations of crystals with flexible monomers. An advantage of this protocol is that it is fully based on first‐principles quantum mechanics and generates tailor‐made FFs suitable for use in subsequent molecular dynamics simulations investigating temperature‐dependent effects. However, empirical intramonomer FFs reparametrized using ab initio data are not yet adequate for CSPs. [ABSTRACT FROM AUTHOR]

Accurate energy data from noncovalent interactions are essential for constructing force fields for molecular dynamics simulations of bio-macromolecular systems. There are two important practical issues in the construction of a reliable force field with the hope of balancing the desired chemical accuracy and working efficiency. One is to determine a suitable quantum chemistry level of theory for calculating interaction energies. The other is to use a suitable continuous energy function to model the quantum chemical energy data. For the first issue, we have recently calculated the intermolecular interaction energies using the SAPT0 level of theory, and we have systematically organized these energies into the ab initio SOFG-31 (homodimer) and SOFG-31-heterodimer datasets. In this work, we re-calculate these interaction energies by using the more advanced SAPT2 level of theory with a wider series of basis sets. Our purpose is to determine the SAPT level of theory proper for interaction energies with respect to the CCSD(T)/CBS benchmark chemical accuracy. Next, to utilize these energy datasets, we employ one of the well-developed machine learning techniques, called the CLIFF scheme, to construct a general-purpose force field for biomolecular dynamics simulations. Here we use the SOFG-31 dataset and the SOFG-31-heterodimer dataset as the training and test sets, respectively. Our results demonstrate that using the CLIFF scheme can reproduce a diverse range of dimeric interaction energy patterns with only a small training set. The overall errors for each SAPT energy component, as well as the SAPT total energy, are all well below the desired chemical accuracy of ~1 kcal/mol. [ABSTRACT FROM AUTHOR]

Symmetry-adapted perturbation theory (SAPT) is a method for computational studies of noncovalent interactions between molecules. This method will be discussed here from the perspective of establishing the paradigm for understanding mechanisms of intermolecular interactions. SAPT interaction energies are obtained as sums of several contributions. Each contribution possesses a clear physical interpretation as it results from some specific physical process. It also exhibits a specific dependence on the intermolecular separation R. The four major contributions are the electrostatic, induction, dispersion, and exchange energies, each due to a different mechanism, valid at any R. In addition, at large R, SAPT interaction energies are seamlessly connected with the corresponding terms in the asymptotic multipole expansion of interaction energy in inverse powers of R. Since such expansion explicitly depends on monomers' multipole moments and polarizabilities, this connection provides additional insights by rigorously relating interaction energies to monomers' properties. [ABSTRACT FROM AUTHOR]

Linear molecules such as CO2 contain a positive π‐hole ring that surrounds C on the molecule's equator. Quantum calculations examine the question as to how many bases can simultaneously bind to this ring. Linear molecules examined are TO2, where T = C, Si, Ge, Sn; bases are NCH and NH3. CO2 engages in the weakest of the tetrel bonds, and can bind up to three NCH and two NH3. Unlike σ‐hole tetrel bonds, Si forms the strongest tetrel bonds, with interaction energies as high as 43 kcal/mol with NH3. But like GeO2, SiO2 can sustain only two bases in its equatorial ring. The π‐hole ring of SnO2 can engage in up to four tetrel bonds with either NCH or NH3, even though these bonds are weaker than those with GeO2 or SiO2. As all of these complexes cast TO2 in the role of multiple electron acceptor, the resulting negative cooperativity makes each successive bond weaker than its predecessor as bases are added, as well as reducing the magnitude of the central molecule's π‐hole. [ABSTRACT FROM AUTHOR]

We perform a study of the molecular anisotropy for the H2⋯H2 van der Waals system using a spherical harmonics expansion. We use six leading stable configurations to construct our analytical potential energy surface (PES) from ab initio calculations guided qualitatively by the symmetry-adapted perturbation theory (SAPT) analyses. We extrapolate the energies of the PES performed at the CCSD(T)/aug-cc-pVnZ (n = 2 and 3) levels to the complete basis set (CBS) limit. To best fit the shallow potential energy surface of each leading configuration with the intermolecular distance, it was employed an extended version of the Rydberg potential. To assess the quality of our extrapolated analytical PES, we calculate the second virial coefficients, which are in relatively good agreement with the experimental data. As a result, the spherical harmonics coefficients obtained might be of considerable relevance in spectroscopy and dynamics applications. [ABSTRACT FROM AUTHOR]

The interactions between carbon dioxide and cluster models of coordinatively unsaturated metal–organic frameworks (MOFs) were studied using a variety of ab initio methods. Three metal species and three organic linkers in four structures were considered in these models as a representation of the tunable nature of MOFs and the potential multireference character of such systems. Common single‐reference methods, such as MP2 and CCSD(T), were compared with multireference methods based on complete active space self‐consistent field theory, going as far as multireference configuration interaction with single and double excitations (MRCISD). Special consideration is taken to avoid issues of size inconsistency in the CI results, where an alternate reference is used in the interaction energy definition. The benchmark values are used to judge the adequacy of a selection of density functionals for the current systems. Symmetry‐adapted perturbation theory (SAPT) decomposition was performed to elucidate the important effects that comprise the binding interactions. The systems proved to have very limited multireference character, and MP2 values were closer to the CCSD(T) benchmark than the more difficult MRCISD results. Though the SAPT total energies prove to be relatively poor approximations to the benchmark interaction energies, they reveal (in most cases) the correct trends with respect to the choice of the metal. The SAPT energy decompositions indicate that the CO2 binding is primarily driven by electrostatics, but induction and dispersion also provide sizable, and quite similar, attractive contributions. Importantly, the small diformate model provides a faithful representation of complexes with large aromatic linkers, both in terms of the total interaction energy and the SAPT decomposition. [ABSTRACT FROM AUTHOR]

This work examines the suitability of meta-GGA functionals for symmetry-adapted perturbation theory (SAPT) calculations. The assessment is based on the term-by-term comparison with the benchmark SAPT variant based on coupled-cluster singles and doubles description of monomers, SAPT(CCSD). Testing systems include molecular complexes ranging from strong to weak and the He dimer. The following nonempirical meta-GGAs are examined: TPSS, revTPSS, MVS, SCAN, and SCAN0 with and without the asymptotic correction (AC) of the exchange-correlation potential. One range-separated meta-GGA functional, LC-PBETPSS, is also included. The AC-corrected pure meta-GGAs (with the exception of MVS) represent a definite progress in SAPT(DFT) compared to pure GGA, such as PBEAC, with their more consistent predictions of energy components. However, none of the meta-GGAs is better than the hybrid GGA approach SAPT(PBE0AC). The SAPT(DFT) electrostatic energy offers the most sensitive probe of the quality of the underlying DFT density. Both SCAN- and TPSS-based electrostatic energies agree with reference to within 5% or better which is an excellent result. We find that SCAN0 can be used in SAPT without the AC correction. The long-range corrected LC-PBETPSS is a reliable performer both for the components and total interaction energies. [ABSTRACT FROM AUTHOR]

Symmetry‐adapted perturbation theory (SAPT) is a well‐established method to compute accurate intermolecular interaction energies in terms of physical effects such as electrostatics, induction (polarization), dispersion, and exchange. With many theory levels and variants, and several computer implementations available, closed‐shell SAPT has been applied to produce numerous intermolecular potential energy surfaces for complexes of experimental interest, and to elucidate the interactions in various complexes relevant to catalysis, organic synthesis, and biochemistry. In contrast, the development of SAPT for general open‐shell complexes is still a work in progress. In the last decade, new developments from several research groups, including the author's, have greatly enhanced the capabilities of SAPT. The new and emerging approaches are designed to make SAPT more widely applicable (including interactions involving multireference systems, complexes in arbitrary spin states, and intramolecular noncovalent interactions), more accurate (enhanced description of intramolecular correlation, a better account of exchange effects, relativistic SAPT, and explicitly correlated SAPT), and more efficient (enhanced density‐fitted implementations, linear‐scaling variants, empirical dispersion, and an implementation on graphics processing units). The new developments open up avenues for SAPT applications to an unprecedented variety of weakly interacting complexes. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsElectronic Structure Theory > Density Functional TheoryMolecular and Statistical Mechanics > Molecular Interactions [ABSTRACT FROM AUTHOR]

Soft anions exhibit surface activity at the air/water interface that can be probed using surface-sensitive vibrational spectroscopy, but the structural implications of this surface activity remain a matter of debate. Here, we examine the nature of anion–water interactions at the air/water interface using a combination of molecular dynamics simulations and quantum-mechanical energy decomposition analysis based on symmetry-adapted perturbation theory. Results are presented for a set of monovalent anions, including Cl−, Br−, I−, CN−, OCN−, SCN−, NO2−, NO3−, and ClOn− (n=1,2,3,4), several of which are archetypal examples of surface-active species. In all cases, we find that average anion–water interaction energies are systematically larger in bulk water although the difference (with respect to the same quantity computed in the interfacial environment) is well within the magnitude of the instantaneous fluctuations. Specifically for the surface-active species Br−(aq), I−(aq), ClO4−(aq), and SCN−(aq), and also for ClO−(aq), the charge-transfer (CT) energy is found to be larger at the interface than it is in bulk water, by an amount that is greater than the standard deviation of the fluctuations. The Cl−(aq) ion has a slightly larger CT energy at the interface, but NO3−(aq) does not; these two species are borderline cases where consensus is lacking regarding their surface activity. However, CT stabilization amounts to

The self‐assembly of chiral organic chromophores is gaining huge significance due to the abundance of supramolecular chirality found in natural systems. We report an interdigitated molecular assembly involving axially chiral octabrominated perylenediimide (OBPDI) which transfers chiral information to achiral aromatic moieties. The crystalline two‐component assemblies of OBPDI and electron‐rich aromatic units were facilitated through π‐hole⋅⋅⋅π donor–acceptor interactions, and the charge‐transfer characteristics in the ground and excited states of the OBPDI cocrystals were established through spectroscopic and theoretical techniques. The OBPDI cocrystals entail a remarkable homochiral segregation of P and M enantiomers of both molecular entities in the same crystal system, leading to twisted double‐racemic arrangements. Synergistically engendered cavities with the stored chiral information of the twisted OBPDI stabilize higher‐energy P/M enantiomers of trans‐azobenzene through non‐covalent interactions. [ABSTRACT FROM AUTHOR]

This work studies the underlying nature of H‐bonds (HBs) of different types and strengths and tries to predict binding energies (BEs) based on the properties derived from wave function analysis. A total of 42 HB complexes constructed from 28 neutral and 14 charged monomers were considered. This set was designed to sample a wide range of HB strengths to obtain a complete view about HBs. BEs were derived with the accurate coupled cluster singles and doubles with perturbative triples correction (CCSD(T))(T) method and the physical components of the BE were investigated by symmetry‐adapted perturbation theory (SAPT). Quantum theory of atoms‐in‐molecules (QTAIM) descriptors and other HB indices were calculated based on high‐quality density functional theory wave functions. We propose a new and rigorous classification of H‐bonds (HBs) based on the SAPT decomposition. Neutral complexes are either classified as "very weak" HBs with a BE ≥ −2.5 kcal/mol that are mainly dominated by both dispersion and electrostatic interactions or as "weak‐to‐medium" HBs with a BE varying between −2.5 and −14.0 kcal/mol that are only dominated by electrostatic interactions. On the other hand, charged complexes are divided into "medium" HBs with a BE in the range of −11.0 to −15.0 kcal/mol, which are mainly dominated by electrostatic interactions, or into "strong" HBs whose BE is more negative than −15.0 kcal/mol, which are mainly dominated by electrostatic together with induction interactions. Among various explored correlations between BEs and wave function‐based HB descriptors, a fairly satisfactory correlation was found for the electron density at the bond critical point (BCP; ρBCP) of HBs. The fitted equation for neutral complexes is BE/kcal/mol =  − 223.08 × ρBCP/a. u. + 0.7423 with a mean absolute percentage error (MAPE) of 14.7%, while that for charged complexes is BE/kcal/mol =  − 332.34 × ρBCP/a. u. − 1.0661 with a MAPE of 10.0%. In practice, these equations may be used for a quick estimation of HB BEs, for example, for intramolecular HBs or large HB networks in biomolecules. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Biotin is well known to be bound with exceptional strength by the avidin class of proteins. This ability comes from a match between the biotin-binding pocket of the protein and the structural elements of biotin, including its ureido and thiolane rings. Here we investigate the solvation shell of biotin in water as revealed by classical force field molecular dynamics with GAFF force field. Snapshots from the classical molecular dynamics were then used to generate microsolvated structures. Details of hydrogen bonding patterns present in these microsolvated structures were studied by symmetry-adapted perturbation theory (SAPT). Interaction energy values for small models of biotin hydrated by 5 or 6 water molecules show that the cooperativity constitutes 15–22% of the total interaction energy and corresponds roughly to formation of one additional hydrogen bond to biotin. The SAPT analysis shows the differences underlying hydrogen bonds of similar strength (with oxygen or sulfur atoms as the hydrogen bond acceptors, and with nitrogen atom playing a dual role of the donor and acceptor). [ABSTRACT FROM AUTHOR]

The mutual interplay between pnicogen-π and tetrel bond in the formation of PF3⊥X-Pyr…SiH3CN ternary complexes has been investigated via a computational chemistry at MP2/aug-cc-pVDZ level of theory. We proved by computational NMR data the effect of electron-withdrawing and electron-donating substituents on 1tJ(N-Si) across 15N...35Si tetrel bonds was investigated at M06-2X/aug-cc-pVDZ levels of theory in PF3⊥CN-Pyr…SiH3CN complex. The nature of the interactions has been studied by means of symmetry-adapted perturbation theory (SAPT) and molecular electrostatic potentials (MEP). The electrostatic interaction played a major role in the change of tetrel bond interaction strength in the X-Pyr…SiH3CN binary systems, whereas the change of pnicogen-π strength in the PF3⊥X-Pyr complexes was caused jointly by the dispersion interactions. Energy decomposition indicates that the percentage of the electrostatic term in the tetrel bond system constitutes in the total attractive binding energies, while the percentage of the dispersion term in the pnicogen bonding constitutes in the attractive binding energies. In addition, atoms in molecules (AIM) and natural bond orbital (NBO) analyses were also performed to unveil the mechanism of these interactions in the title complexes. [ABSTRACT FROM AUTHOR]

In a recent publication [Nature Chemistry, 6, 727 (2014)] the synthesis and properties of a new all-boron fullerene analog, B 40 , have been reported, and a possibility of utilizing the B 40 molecule as a hydrogen storage has been postulated. Therefore, in this contribution we study the stability of endo- and exohedral complexes with the hydrogen molecule and several other small molecules, such as N 2 , H 2 O, and CO 2 . The examination of binding and interaction energies obtained by symmetry-adapted perturbation theory and by supermolecular approaches shows that among the studied endohedral complexes only the one with H 2 inside the cage is possibly weakly stabilized by the complexation, while all other molecules clearly exhibit too large repulsion, which cannot be counterweighted by attractive components of the interaction energy. An addition of the zero-point vibrational correction to the H 2 @B 40 binding energy changes the balance of the attractive and repulsive contributions in favor of repulsion, so that finally also this endohedral complex is thermodynamically unstable at zero Kelvin. The exohedral minima are stable in all the cases, and are mostly bound by dispersion. [ABSTRACT FROM AUTHOR]

A molecular fragmentation method has been used to analyze the intramolecular interactions in the three molecules coupled diamantane, hexaphenylethane, and all-meta- tert-butyl substituted hexaphenylethane. The significance of these systems lies in the fact, that steric crowding effects enable a stabilization of the central carbon bond that possesses an extended length (1.6 to 1.7 Å) beyond conventional carbon-carbon bonds due to the steric repulsion of the attached hydrocarbon groups. The total stability of these molecules therefore depends on a delicate balance between attractive interaction forces on the one hand and on repulsive forces on the other hand. We have quantified the different interaction energy contributions using symmetry-adapted perturbation theory based on a density functional theory description of the monomers. It has been found that the attractive dispersion interactions increase more strongly with the level of crowding in the systems than the counteracting exchange interactions. This shows that steric crowding effects can have a significant impact on the structure and stability of large and branched molecules. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A method for computing quasi-relativistic two-component dispersion energies is developed and implemented in the TURBOMOLE program package. The method is based on the Casimir–Polder formula for dispersion energies, which occurs in symmetry-adapted perturbation theory. The method is applied to evaluate the dispersion energies of a small set of van der Waals complexes involving heavy elements such as gold, mercury and bismuth. [ABSTRACT FROM PUBLISHER]

The multi-configurational ansatz of valence-bond theory may serve as basis for calculating intermolecular interaction energies in a non-orthogonal basis. We look in the present contribution at the possibility to obtain the 1st-order electrostatic interactions from breathing-orbital valence-bond densities, and the 2nd-order dispersion energy from dipole-dipole interactions. The discussion is based on numerical results for the interaction of two N 2 O molecules. [ABSTRACT FROM AUTHOR]

Random-phase-approximation (RPA) methods have proven to be powerful tools in electronic-structure theory, being non-empirical, computationally efficient and broadly applicable to a variety of molecular systems including small-gap systems, transition-metal compounds and dispersion-dominated complexes. Applications are however hindered due to the slow basis-set convergence of the electron-correlation energy with the one-electron basis. As a remedy, we present approximate explicitly-correlated RPA approaches based on the ring-coupled-cluster-doubles formulation including exchange contributions. Test calculations demonstrate that the basis-set convergence of correlation energies is drastically accelerated through the explicitly-correlated approach, reaching 99% of the basis-set limit with triple-zeta basis sets. When implemented in close analogy to early work by Szabo and Ostlund [36], the new explicitly-correlated ring-coupled-cluster-doubles approach including exchange has the perspective to become a valuable tool in the framework of symmetry-adapted perturbation theory (SAPT) for the computation of dispersion energies of molecular complexes of weakly interacting closed-shell systems. [ABSTRACT FROM AUTHOR]

The conventional surface integral formulaJsurf[Φ] and an alternative volume integral formulaJvar[Φ] are used to compute the asymptotic exchange splitting of the interaction energy of the hydrogen atom and a proton employing the primitive function Φ in the form of its truncated multipole expansion. Closed-form formulas are obtained for the asymptotics ofJsurf[ΦN] andJvar[ΦN], where ΦNis the multipole expansion of Φ truncated after the 1/RNterm,Rbeing the internuclear separation. It is shown that the obtained sequences of approximations converge to the exact result with the rate corresponding to the convergence radius equal to 2 and 4 when the surface and the volume integral formulas are used, respectively. When the multipole expansion of a truncated,Kth order polarisation function is used to approximate the primitive function, the convergence radius becomes equal to unity in the case ofJvar[Φ]. At low order, the observed convergence ofJvar[ΦN] is, however, geometric and switches to harmonic only at certain value ofN=Ncdependent onK. An equation forNcis derived which very well reproduces the observedK-dependent convergence pattern. The results shed new light on the convergence properties of the conventional symmetry-adapted perturbation theory expansion used in applications to many-electron diatomics. [ABSTRACT FROM PUBLISHER]

Highlights: [•] The properties of short H ⋯ H contact in nicotinamide crystal were characterized. [•] The hydrogen bonds by means of periodic DFT calculations and AIM theory were investigated. [•] The nature of interactions using variational–perturbational scheme and DFT methods was analyzed. [ABSTRACT FROM AUTHOR]

This work characterizes eight stationary points of the P2 dimer and six stationary points of the PCCP dimer, including a newly identified minimum on both potential energy surfaces. Full geometry optimizations and corresponding harmonic vibrational frequencies were computed with the second-order Møller-Plesset (MP2) electronic structure method and six different basis sets: aug-cc-pV XZ, aug-cc-pV( X+ d)Z, and aug-cc-pCV XZ where X = T, Q. A new L-shaped structure with C2 symmetry is the only minimum for the P2 dimer at the MP2 level of theory with these basis sets. The previously reported parallel-slipped structure with C2 h symmetry and a newly identified cross configuration with D2 symmetry are the only minima for the PCCP dimer. Single point energies were also computed using the canonical MP2 and CCSD(T) methods as well as the explicitly correlated MP2-F12 and CCSD(T)-F12 methods and the aug-cc-pV XZ ( X = D, T, Q, 5) basis sets. The energetics obtained with the explicitly correlated methods were very similar to the canonical results for the larger basis sets. Extrapolations were performed to estimate the complete basis set (CBS) limit MP2 and CCSD(T) binding energies. MP2 and MP2-F12 significantly overbind the P2 and PCCP dimers relative to the CCSD(T) and CCSD(T)-F12 binding energies by as much as 1.5 kcal mol−1 for the former and 5.0 kcal mol−1 for the latter at the CBS limit. The dominant attractive component of the interaction energy for each dimer configuration was dispersion according to several symmetry-adapted perturbation theory analyses. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This work characterizes eight stationary points of the P2 dimer and six stationary points of the PCCP dimer, including a newly identified minimum on both potential energy surfaces. Full geometry optimizations and corresponding harmonic vibrational frequencies were computed with the second-order Møller-Plesset (MP2) electronic structure method and six different basis sets: aug-cc-pV XZ, aug-cc-pV( X+ d)Z, and aug-cc-pCV XZ where X = T, Q. A new L-shaped structure with C2 symmetry is the only minimum for the P2 dimer at the MP2 level of theory with these basis sets. The previously reported parallel-slipped structure with C2 h symmetry and a newly identified cross configuration with D2 symmetry are the only minima for the PCCP dimer. Single point energies were also computed using the canonical MP2 and CCSD(T) methods as well as the explicitly correlated MP2-F12 and CCSD(T)-F12 methods and the aug-cc-pV XZ ( X = D, T, Q, 5) basis sets. The energetics obtained with the explicitly correlated methods were very similar to the canonical results for the larger basis sets. Extrapolations were performed to estimate the complete basis set (CBS) limit MP2 and CCSD(T) binding energies. MP2 and MP2-F12 significantly overbind the P2 and PCCP dimers relative to the CCSD(T) and CCSD(T)-F12 binding energies by as much as 1.5 kcal mol−1 for the latter at the CBS limit. The dominant attractive component of the interaction energy for each dimer configuration was dispersion according to several symmetry-adapted perturbation theory analyses. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]−1 for the latter at the CBS limit. The dominant attractive component of the interaction energy for each dimer configuration was dispersion according to several symmetry-adapted perturbation theory analyses. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The strength and nature of the halogen-bond interactions in CCl3F···O3complexes were examined by means ofab initioquantum-chemical calculations and symmetry-adapted perturbation theory (SAPT). Our calculations predict a trifurcated C–Cl···O interaction for the global minimum of CCl3F···O3complex and several local minima, differing slightly in energy, separated by very low barriers. The calculations, which include a rigorous decomposition of the interaction energies, also indicate that the interaction of CCl3F molecule with O3is characterised by contributions from both electrostatic and dispersion energies, with the contribution of the latter being dominant. The evaluated SAPT interaction energies for the CCl3F···O3complexes are generally in good agreement with those obtained using the supermolecule CCSD(T) method, suggesting that SAPT is a proper method to study the intermolecular interactions in these complexes. [ABSTRACT FROM AUTHOR]

Symmetry-adapted perturbation theory (SAPT) with intramonomer electron correlation described by coupled cluster theory limited to single and double excitations was applied to 21 noncovalent complexes in their minimum geometries. The resulting benchmark contributions to the interaction energy were utilized to examine the accuracy of a more approximate variant of the SAPT method, where interacting molecules are described by density functional theory (DFT) with different functionals, like LDA, PBE, B3LYP, PBE0, M05, M05-2X, M06, and M06-2X (in all cases the asymptotic correction for the exchange-correlation functional has been utilized). Average errors for individual energy components of SAPT(DFT) are not larger than 10% for best functionals under study. Among the tested functionals PBE0, M05, and B3LYP should be especially recommended for the SAPT(DFT) approach. The M06 functional gives the largest errors with respect to SAPT(CCSD) and should not be used for describing intramonomer correlation in SAPT. [ABSTRACT FROM AUTHOR]

A series of substituted naphthalimides were synthesized and intercalated into the d(GCGCGCGC)2, and an experimental ΔTm value was obtained. Two-parameter QSAR analyses were performed to generate a theoretical ΔTm value. Although by no means exhaustive in terms of parameter selection, the correlations did not yield statistics that indicated the models met the threshold for significance at the 95% confidence level. Rather than continue with an exhaustive search of all possible QSAR parameters, a one-parameter QSAR analysis was performed utilizing a novel arene-arene stacking parameter, designated Ππ, developed from Symmetry-Adapted Perturbation Theory (SAPT) energy decomposition studies of calculated benzene-substituted benzene dimer binding energies. The QSAR analysis using the Ππ stacking parameter yielded statistics suggesting the model was significant at the 95% confidence level. The approach of developing a novel QSAR parameter via SAPT calculations, rather than exhaustively searching all traditional QSAR parameters, is presented both as a new approach for QSAR studies and as a unique application of SAPT. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

It is shown that the exchange-dispersion energy contribution of symmetry-adapted intermolecular perturbation theory (SAPT) can be evaluated without invoking the single-exchange approximation in the case of single-determinant ground-state references. A succinct expression is derived which allows for efficient implementation. Making use of the corresponding exchange-induction contribution, obtained recently, this enables DFT-SAPT calculations, i.e., SAPT based on a density-functional theory description of the monomers, without an expansion in orders of the intermonomer overlapS. The approach is used to test the quality of theS2or single-exchange approximation for the systems He2, Ar2, N2–Ne, H2O–Ar, (H2O)2and LiF, i.e., van der Waals and hydrogen-bridged complexes as well as an ionic molecule. While employing theS2approximation for the exchange-dispersion contribution is found to have minor impact on total SAPT interaction energies, its use to evaluate the exchange-induction contribution significantly affects the quality of the repulsive branches of the potential energy curves for the interacting partners. Adding appropriate Hartree–Fock level estimates of higher-order induction plus exchange-induction energies, however, restores good agreement with complete basis set limit coupled-cluster results. [ABSTRACT FROM PUBLISHER]

In this work, the characteristics of the O–H…O interactions in aspirin…(water)n = 1 − 3as well as in the fluorine-substituted aspirin…(water)n = 1 − 3complexes were studied by means of computational methods: symmetry-adapted perturbation theory, atoms in molecules (AIM) and natural bond orbital approaches. It is found that the cooperativity effect enhances significantly the O–H…O hydrogen bond; in some of the cases one can detect the covalent nature of hydrogen bonding. The magnitude of interaction energies of complexes increases with increasing the size of water cluster. In all the complexes studied herein, the electrostatic interaction between aspirin or fluorine-substituted aspirin and water is the main attractive force, and its contribution may be seven times as large as the corresponding contribution from dispersion. The AIM theory suggests for stronger O–H…O hydrogen bonds, the electronic energy density at the H…O bond critical point is negative and may be attributed to the partly covalent interaction. [ABSTRACT FROM AUTHOR]

We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene-BX complexes, where X = H, OH, NH, CH, CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B-C interaction due to the short B-C distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH > OH > CH > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with ∇ ρ >0, the B-C bond critical points (BCPs) are characterized by a reasonably large value of the electron density ( ρ) and H <0, indicating that the potential energy overcomes the kinetic energy density at BCP and the B-C bond is a polar covalent bond. [ABSTRACT FROM AUTHOR]

A distributed point polarizable model potential for carbon dioxide, with explicit terms for charge penetration and induction, is introduced. This model potential accurately describes the structures and interaction energies of small (CO) clusters and also gives the second virial coefficients and radial distribution functions of supercritical CO in excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

Quantum mechanics calculations were applied to investigate the NH···O hydrogen bonding properties in linear (urea)n=1–10 clusters. We investigated geometries, binding energies, and 17O chemical shielding tensors of urea clusters, by means of MP2 and DFT methods. The charge‐transfer character of the urea clusters was estimated using Natural Bonding Orbital characteristics. It was found that the cooperativity effects enhance significantly the NH···O hydrogen bond from −33.08 (dimer) to −47.67 kJ/mol (decamer). The n‐dependent trend of 17O shielding tensors was reasonably correlated with cooperative effects in rCO bond distance. To deepen the nature of the interaction in urea clusters, the scheme of decomposition of the interaction energies was applied using Morokuma analysis and a variant of symmetry‐adapted perturbation theory (SAPT) based on DFT description of monomers, referred to as SAPT‐DFT. The SAPT‐DFT analysis of the interaction energy components indicates that the electrostatic and dispersive interactions are the most important attractive terms in the urea dimer. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Theoretical investigations of the induction interaction between closed-shell molecules which fully account for the orbital relaxation effects are presented. Explicit expressions for the third-order induction energy in terms of molecular integrals and orbital energies are given and implemented within the sapt2008 program for symmetry-adapted perturbation theory (SAPT) calculations. Numerical investigations for the He-He, He-LiH, Ar-Ar, H-CO, HO-HO, and HO-NH model dimers show that the orbital relaxation increases the third-order induction interaction by 15 to 50% at near-equilibrium geometries, with the largest effect observed for complexes involving highly polar monomers. At large intermonomer separations, the relaxed third-order induction energy perfectly recovers the difference $$\delta E^{\rm HF}_{\rm int}$$ between the Hartree-Fock interaction energy and the sum of the uncorrelated SAPT contributions through second order in the intermolecular interaction operator. At the near-equilibrium geometries, the sum of the relaxed third-order induction and exchange-induction energies reproduces, however, only a small fraction (6 to 15%) of $$\delta E^{\rm HF}_{\rm int}$$ for the nonpolar systems and about 40 to 60% for the polar ones. A comparison of the complete SAPT calculations with the coupled-cluster treatment with single, double, and noniterative triple excitations [CCSD(T)] suggests that the pure SAPT approach with all the available third-order corrections is more accurate for nonpolar systems while for the polar ones the hybrid approach including $$\delta E^{\rm HF}_{\rm int}$$ gives better results. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been performed on six halogen-hydride halogen bonded complexes with F3CCl or F3CBr as the halogen donor and metal hydride (HLi, HBeH and HMgH) as the halogen acceptor. At the MP2/6-311++G(d,p) level, the interaction strength spans from 2.62 to 17.68 kJ mol-1. The C-Cl and C-Br bonds are contracted. However, no evident blue shift accompanies this contraction. The H-Li bond is also contracted, but the H-He and H-Mg bonds are lengthened. However, a blue shift occurs for all these bond-stretching vibrations. These properties were analysed using the theory of natural bond orbital (NBO) and atoms in molecules (AIM). A symmetry-adapted perturbation theory (SAPT) analysis was also carried out to unveil the nature of this novel interaction. It is demonstrated that the electrostatic interaction plays a main role in the interaction, although induction and dispersion interactions are also important. [ABSTRACT FROM AUTHOR]

The halogen bonding complexes H2O ⋯ M (M = F2, ClF, and CF4) in comparison with the hydrogen bonding H2O ⋯ HF complex are studied by high-level ab initio calculations and electron topological atoms-in-molecules (AIM) analyses. The basis set superposition error corrections are important to predict if the structures are in good agreement with the experimental results. Both the CCSD(T)/aug-cc-pVTZ calculations and the AIM analyses indicate a interaction strength order: H2O ⋯ HF > H2O ⋯ ClF ⋯ H2O ⋯ F2 ⋯ H2O ⋯ CF4, with the interaction energies –7.91, –4.16, –1.11, and –1.05 kcal/mol, respectively. The symmetry-adapted perturbation theory analyses have been carried out towards understanding of the nature of the halogen bonding interactions in the complexes H2O ⋯ M (M = F2, ClF, andCF4), where the exchange energies are the predominant repulsive components. For the complexes involving polar monomers, the hydrogen bonding H2O ⋯ HF and the halogen bonding H2O ⋯ ClF, the largest attractive contributions are the electrostatic energies. However, in H2O ⋯ F2 and H2O ⋯ CF4, the attractive dispersion energies become more important, and the induction energy in the former complex is a little higher than that in the latter. In contrary to the red-shifts of H–F, Cl–F, and F–F bond stretching vibrational frequencies in the complexes H2O ⋯ M (M = HF, ClF, andF2), the blue-shifts are predicted for C–F bonds neighboring water in H2O ⋯ CF4. [ABSTRACT FROM AUTHOR]

The halogen bonding complexes H2O ⋯ M (M = F2, ClF, and CF4) in comparison with the hydrogen bonding H2O ⋯ HF complex are studied by high-level ab initio calculations and electron topological atoms-in-molecules (AIM) analyses. The basis set superposition error corrections are important to predict if the structures are in good agreement with the experimental results. Both the CCSD(T)/aug-cc-pVTZ calculations and the AIM analyses indicate a interaction strength order: H2O ⋯ HF > H2O ⋯ ClF ⋯ H2O ⋯ F2 ⋯ H2O ⋯ CF4, with the interaction energies –7.91, –4.16, –1.11, and –1.05 kcal/mol, respectively. The symmetry-adapted perturbation theory analyses have been carried out towards understanding of the nature of the halogen bonding interactions in the complexes H2O ⋯ M (M = F2, ClF, andCF4), where the exchange energies are the predominant repulsive components. For the complexes involving polar monomers, the hydrogen bonding H2O ⋯ HF and the halogen bonding H2O ⋯ ClF, the largest attractive contributions are the electrostatic energies. However, in H2O ⋯ F2 and H2O ⋯ CF4, the attractive dispersion energies become more important, and the induction energy in the former complex is a little higher than that in the latter. In contrary to the red-shifts of H–F, Cl–F, and F–F bond stretching vibrational frequencies in the complexes H2O ⋯ M (M = HF, ClF, andF2), the blue-shifts are predicted for C–F bonds neighboring water in H2O ⋯ CF4. [ABSTRACT FROM AUTHOR]