Localized Molecular Orbital Energy Decomposition Analysis Research Articles

Boiling, critical, and freezing temperatures in light of molecular descriptors: correlation and causation.

In the pursuit of tracking some physicochemical properties of fluids down to the molecular level, ab initio molecular surface analyses were performed on 169 molecules. This included electrostatic potential (EP), average local ionization energy (ALIE), and electron localization function (ELF) mapped onto an electron density isosurface value of 0.001 au. Using stepwise linear regression (SLR) analysis, it was found that besides the well-studied EP, ALIE and ELF played important roles in determining the normal boiling and freezing points and critical temperatures of fluids. Apparently, the ALIE and ELF were relevant to the attractive polarization forces and repulsive Pauli forces, respectively, between molecules. To further demonstrate and rationalize this assumption, a localized molecular orbital energy decomposition analysis (LMO-EDA) was carried out. In the LMO-EDA analysis, the complexes of the helium atom, He, and ClCl, ClBr, ClI, OCO, OCS, OCSe, and CO/OC molecules were investigated, where the helium atom faced different molecular sites in each molecule. Fortunately, the results showed that lower the ALIE value on a molecular site, the stronger (i.e., more attractive) the polarization interaction energy. The results also indicated that higher the ELF value on a molecular site, the stronger (i.e., more repulsive) the Pauli interaction. The work is aimed to present novel molecular-based rationales to physical chemists, chemical engineers, and materials scientists.

Influence of the metal - support and metal - metal interactions on Pd nucleation and NO adsorption in a Pd4/γ-Al2O3 (110D) model.

The role played by the metal - support (MSI) and metal - metal (MMI) interactions on two important processes in controlling the catalyst performance - nucleation and molecular adsorption - has been investigated using density functional theory (DFT), by means of B3LYP functional, combined with localized molecular orbital energy decomposition analysis (LMOEDA), and natural bond orbital (NBO) calculations, with aid of a Pd4/γ-alumina (110D) model (Pd4/Al13O23H7). Our results indicate the occurrence of an electronic metal - support interaction (EMSI) which induces a most intense charge transfer in the Pd4 → γ-alumina backdonation direction, most expressive in Pd → Al, promoting an electronic redistribution within the units and attenuating the MMI. Nevertheless, the MSI/MMI synergistic effect seems to favor slightly the nucleation of a fifth palladium atom, leading to a distorted square pyramidal arrangement for Pd5. The LMOEDA analysis points to a mostly covalent character in the Pd - Al bonds, whereas the Pd - O bonds are mainly electrostatic in nature. The palladium atoms deposited on oxygen anions are the acid centers, where both NO molecule and an additional palladium atom anchor more strongly. In addition, the MSI/MMI effect, through the electronic and geometric contributions, drives the adsorption of the NO molecule to the mode which most favors the Pd → NO (4dz2 → 2π*) backdonation (bridge mode). MSI and MMI effects on the nature of the Pd - O (electrostatic) and Pd - Al (covalent) bonds, charge transfer into Pd4/γ-Al2O3 (110D) interface (back donation) and preferential site for adsorption of a single NO molecule and an additional Pd atom (Pd - O).

Estimation of resonance assisted hydrogen bond (RAHB) energies using properties of ring critical points in some dihydrogen-bonded complexes

Intramolecular hydrogen bond (IHB) interactions have investigated in aza-boron-hydrogen rings after formation of dihydrogen bond (DHB) interactions with some substituted aza-boron-hydrogen molecules. These molecules include electron-donating and electron-withdrawing groups. The IHB energies in the dihydrogen-bonded complexes have estimated using a method based on properties of ring critical points (RCPs). There is linear relationship between results of this method and molecular tailoring approach (MTA). Geometrical parameters, spectroscopic information, electronic properties based on atoms in molecules (AIM) method, and natural bond orbital (NBO) analysis have used to find effects of DHB on strength of the IHB interaction. Moreover, aromaticity of resonance-assisted hydrogen bond (RAHB) rings have evaluated using the para delocalization index (PDI), the aromatic fluctuation index (FLU), the average two center index (ATI), and the nucleus-independent chemical shift (NICS) to find relation between π-electron delocalization (π-ED) and properties of these rings. Results show that DHB leads to increase of strength of the IHB interaction. In addition, the PDI benchmark has the best correlation with the IHB descriptors. Additionally, localized molecular orbital energy decomposition analysis (LMO-EDA) reveals that the key components of interaction energies are exchange and electrostatic energy, respectively. Finally, new relations obtained for estimation of the IHB energies based on RCP characteristics and quantum mechanical descriptors.

The Importance of Strain (Preorganization) in Beryllium Bonds.

In order to explore the angular strain role on the ability of Be to form strong beryllium bonds, a theoretical study of the complexes of four beryllium derivatives of ortho closo-carboranes with eight molecules (CO, N2, NCH, CNH, OH2, SH2, NH3, and PH3) acting as Lewis bases has been carried out at the G4 computational level. The results for these complexes, which contain besides Be other electron-deficient elements, such as B, have been compared with the analogous ones formed by three beryllium salts (BeCl2, CO3Be and SO4Be) with the same set of Lewis bases. The results show the presence of large and positive values of the electrostatic potential associated to the beryllium atoms in the isolated four beryllium derivatives of ortho-carboranes, evidencing an intrinsically strong acidic nature. In addition, the LUMO orbital in these systems is also associated to the beryllium atom. These features led to short intermolecular distances and large dissociation energies in the complexes of the beryllium derivatives of ortho-carboranes with the Lewis bases. Notably, as a consequence of the special framework provided by the ortho-carboranes, some of these dissociation energies are larger than the corresponding beryllium bonds in the already strongly bound SO4Be complexes, in particular for N2 and CO bases. The localized molecular orbital energy decomposition analysis (LMOEDA) shows that among the attractive terms associated with the dissociation energy, the electrostatic term is the most important one, except for the complexes with the two previously mentioned weakest bases (N2 and CO), where the polarization term dominates. Hence, these results contribute to further confirm the importance of bending on the beryllium environment leading to strong interactions through the formation of beryllium bonds.

Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions

Intra- and intermolecular hydrogen bonding interactions in some pyridine-based complexes that have R groups without (H, –C2H5, and –C4H9) and with (−C2H3, –C4H5, –C6H7, and –C8H9) π-conjugated system were investigated using quantum mechanical calculations to know role of resonance on strength of interactions. Geometrical parameters and electronic properties based on atoms in molecules (AIM) analysis were studied to interpret the interactions. Also, aromaticity of the rings of the complexes was evaluated using aromatic fluctuation index (FLU) and para-delocalization index (PDI) to connect the mentioned benchmark to energy of the hydrogen bond interactions. Indeed, localized molecular orbital energy decomposition analysis (LMO-EDA) was employed to realize contribution of components of energy in stability of the complexes.

Basicity of N-heterocyclic carbene and its main-group analogues

In this study, the N-heterocyclic carbene (NHC) imidazole-2-ylidene and its analogues species of group13-15 are considered to study their basicity. Proton affinity (PA) and gas phase basicity (GPB) of each species are calculated at the B3LYP/def2-TZVP level of theory. It is found that PA and GPB decrease down a group and along a period. The acidity of the conjugate acid (pKa) of the NHC analogues are computed in solution giving comparable result to the gas phase ones. The binding energies (ΔEbind) of the adduct formation of the carbene analogues with BH3, BF3 and BCl3 are computed at the same level of theory and follows the same trend. Further interaction energies (ΔEint) of the borane adduct are calculated using localized molecular orbital energy decomposition analysis (LMO-EDA) showing electrostatic (ΔEel) as the dominant factor. Donor-acceptor interaction has been justified from Charge decomposition and Natural bond orbital (NBO) analysis.

Structure, DFT based investigations on vibrational and nonlinear optical behavior of a new guanidinium cobalt thiocyanate complex

This paper reports the crystal growth and structure of a newly synthesized hybrid organic-inorganic compound (CH6N3)2[Co (NCS)4].H2O by means of a joint experimental and theoretical study. Single-crystal X-ray diffraction reveals that this compound crystallizes in the noncentrosymmetric P21212 space group. The 3D framework of the crystal structure is formed by hydrogen-bonded cations of (CH6N3)+, [Co (NCS)4]2− anions and water molecules. UV-Visible reveals an indirect allowed optical transition with energy gap Eg = 3.41 eV. The optimized molecular structure, harmonic vibrational frequencies, static and frequency-dependent nonlinear optical (NLO) parameters were calculated by density functional theory with and without dispersion corrections. A good consistency for the structure, as well as IR and Raman spectra, is found between the calculated and experimental results. A detailed interpretation of the vibrational modes was carried out and a total assignment was performed on the basis of the potential energy distribution (PED) contribution. Moreover, the inter-ionic interaction energy was evaluated and a decomposition analysis was performed by localized molecular orbital energy decomposition analysis (LMO-EDA) method. The calculated NLO parameters compared to urea as a reference show that the title compound can be a good candidate for NLO applications.

Complexes of damirone A/C, batzelline A/D, makaluvamine O and makaluvone with guanidinium and magnesium cations: a theoretical study

Among physiologically active compounds isolated from marine organisms, the pyrroloquinoline alkaloids (PQAs) family consisting of damirone A/C, batzelline A/D, makaluvamine O and makaluvone exhibit numerous biological activities derived from the inimitable highly-fused structures. Their structural and electronic properties were investigated through intramolecular interactions, electron affinities (EA), reduction potentials (E°) and complexation of compounds with magnesium and guanidinium cations (ionic and hydrogen bond interactions) using quantum mechanical calculations in the gas phase and solution. For both series of complexes, the most and least stable ones correspond to damirone A and batzelline D, respectively. The energy data, geometrical parameters, and the minima of electrostatic potentials (Vmin) are in good correlation with the results of population analyses. The localized molecular orbital energy decomposition analyses (LMO-EDA) demonstrate that the electrostatic interaction is the most important stabilizing component. The EA values are positive in the gas phase and solution, and are evaluated with the increase in the dielectric constant of solvent. Increase in the EA values and decrease in the E° values are observed after complexation with guanidinium and magnesium cations. Those changes are higher for electron-rich compounds compared to electron-deficient ones, containing halogen substituents.

A theoretical insight into several common anion recognitions based on double‐dentate hydrogen bond and anion‐π coexistence

AbstractAnion recognitions of a pincer‐like receptor (N,N'‐bis‐(2‐fluoro‐benzoyl‐oxyethyl)‐urea, AR) for several common inorganic anions (F−, Cl−, Br−, I−, CN−, and SO42−) were theoretically explored and predicted at a molecular level in this paper. Geometric configurations of the complex (AR@X (X = F−, Cl−, Br−, and SO42−)) show that two N─H groups as a claw and two ─C6H4F rings on AR as a pair of tweezers simultaneously interact with the captured anions through cooperative double‐dentate hydrogen bond and double‐side anion‐π interactions. However, there is no anion‐π contact between AR and I− ion in AR@I− complex. In the system of AR@CN−, a stable single‐side CN−‐π is possible. The structure of stable 2:1 complex formed with two AR receptors and one SO42− is also predicted. The binding energies and thermodynamic information indicate that the recognitions of the above six anions by AR in the vacuum are spontaneously enthalpy‐driven and entropy‐opposed. The binding energy ΔEcp between SO42− and AR is higher than 340 kJ mol−1, suggesting that AR is an ideal selective anion receptor for SO42−. Additionally, energy decomposition analysis based on localized molecular orbital energy decomposition analysis (LMO‐EDA) was performed. Electronic properties and behaviors of the present systems were further discussed according to calculations on frontier molecular orbital, UV‐vis spectra, and visualized weak interaction regions.

Investigation of intramolecular hydrogen bonding in conjunction with cation-π interactions in complexes involving 4-substituted-8-hydroxyquinolines

Intramolecular hydrogen bonding interactions together with non-covalent cation-π interactions of the Na+ cation in 4-substituted-8-hydroxyquinolines were investigated using quantum mechanical calculations to know results of reciprocal effects of these interactions. Also, cation-π interactions of Na+ cation on 4-substituted-quinolines as a similar system without intramolecular hydrogen bonding were considered to compare binary complexes Na+-X-8-hydroxyquinolines and Na+-X-quinolines (where X is used as a replacement for 4-substituted and X = OH, CH3, H, F, Cl, CF3, and CN). Geometrical parameters, Hammett constants, and electronic properties were studied to interpret the binding energies. A new formulation was proposed to compute energy of intramolecular hydrogen bonding interactions based on atoms in molecules (AIM) analysis and properties of electron charge densities at ring critical points (RCPs). Also, population analysis was performed using natural bond orbital (NBO) method to find role of donor-acceptor interactions on stability of the complexes. Indeed, localized molecular orbital energy decomposition analysis (LMO-EDA) was employed to realize contribution of components of energy in stability of the complexes.

Theoretical insight to intermolecular hydrogen bond interactions between methyl N-(2-pyridyl) carbamate and acetic acid: substituent effects, cooperativity and energy decomposition analysis

In the present work, the hydrogen bond (HB) interactions between substituted syn and anti rotamers of methyl N-(2-pyridyl) carbamate and acetic acid were investigated using quantum mechanical (QM) calculations. The rotamers have two typical active sites to form hydrogen bonds with acetic acid, such that four stable complexes are found on the potential energy surface. The complexes in which the oxygen atom of carbamate acts as proton acceptor are stabilized by EWSs and are destabilized by EDSs. The trend in the effects of substituents is reversed in the other two complexes, in which the nitrogen atom of ring is involved in the interaction. According to energy data, the substituent effects on the interaction energy can be expressed by Hammett constants. The natural resonance theory (NRT) model was used to investigate the charge distribution on the carbamate group and to discuss the interaction energies. The individual HB energies were estimated to evaluate their cooperative contributions on the interaction energies of the complexes. In addition, the localized molecular orbital energy decomposition analyses (LMO-EDA) demonstrate that the electrostatic interactions are the most important stabilizing components of interactions.

Acidities under the Perspective of Energy Decomposition Analysis.

The rationalization of acid/base behavior is a central concern for chemistry and related fields. In this work, we describe an alternative approach toward the understanding of gas phase acidities based on the localized molecular orbital energy decomposition analysis (LMOEDA) method. Upon partitioning the molecules (and the corresponding anions) over the X-OH (or X-O-) bond, we have observed a perfect correlation between the interaction energy of the two fragments and the acidity, as given by the energy difference between the anion and the neutral molecule. On the basis of this correlation, acidities could be interpreted according to the energy components provided by LMOEDA, namely, electrostatic, exchange repulsion, polarization, and dispersion. For example, alkyl groups increase the gas phase acidities of alcohols mainly due to electrostatic and polarization interactions. Carboxylic acids are stronger acids than alcohols through the ability of oxygen to stabilize the extra charge formed in the anion (electrostatic interactions) and also through a decrease of exchange repulsions between the two fragments. Polarization interaction (orbital relaxation) also plays an important role. Electrostatic and polarization interactions dominate the enhanced acidity of sulfuric acid over ethanol. Electrostatic and polarization interactions are also responsible for the higher acidity of sulfuric over boric acid. The anomalous behavior of formic acid compared to acetic, propionic, and butyric acids is also explained. The examples worked in this report evince the still unexplored potential of energy decomposition to the comprehension of acid/base phenomena.

Energy decomposition analysis of the interactions in adduct ions of acetophenone and Na+, NH4+ and H+ in the gas phase

The physical origins of the interactions in the acetophenone cation adducts [M+Na]+, [M+NH4]+, and [M+H]+ were explored by localized molecular orbital-energy decomposition analysis and density functional theory. The analyses highlighted the differences in the interactions in the three adduct ions. Electrostatic energy was important in [M+Na]+ and there was little change in the acetophenone orbital shape. Both electrostatic and polarization energy were important in [M+NH4]+, and a considerable change in the orbital shape occurred to maximize the strength of the hydrogen bond. Polarization energy was the major attractive force in [M+H]+.

Lewis acid-base behavior of hypervalent halogen fluorides in gas phase

Theoretical studies on Lewis acid-base behavior of hypervalent halogen fluorides, F3X and F5X (X = Cl, Br, I) have been instrumental in guiding this work. We have also examined whether the hole-lump concept explains the formation of the F5X∙∙∙CO complexes. Calculations of proton affinities (PA) and gas-phase basicity (GB) on hypervalent halogen fluorides show that F3X and F5X molecules can act as Lewis bases in gas phase. Moreover, theoretical calculations indicate that F3X and F5X molecules can act as Lewis acids forming stable complexes with a Lewis base as CO. The quantum theory of atoms in molecules (QTAIM) shows that the electrostatic interaction between the lone pair of the Lewis base (CO) and nucleus of the hypervalent halogen atom (X) plays a key role in stabilizing and determining the optimal geometry of the F5X∙∙∙CO complexes, as in conventional XBs. The localized molecular orbital energy decomposition analysis (LMOEDA) reveals that electrostatic component plays an important role in the stability of the FnX···CO complexes.

Anion Recognition Based on a Combination of Double-Dentate Hydrogen Bond and Double-Side Anion-π Noncovalent Interactions.

Anion recognitions between common anions and a novel pincer-like receptor (N,N'-bis(5-fluorobenzoyloxyethyl)urea, BFUR) were theoretically explored, particularly on geometric features of the BFUR@X (X = F-, Cl-, Br-, I-, CO32-, NO3-, and SO42-) systems at a molecular level in this work. Complex structures show that two N-H groups as a claw and two -C6F5 rings on BFUR as a pair of tweezers simultaneously interact with captured anions through cooperative double-dentate hydrogen bond and double-side anion-π interactions. The binding energies and thermodynamic information indicate that the recognitions of the seven anions by BFUR in vacuum are enthalpy-driven and entropy-opposed, which occur spontaneously. Although the binding energy ΔEcp between F- and BFUR is relatively high (289.30 kJ·mol-1), ΔEcp, ΔG, and ΔH of the recognition for CO32- and SO42- are much larger than the cases of F-, Cl-, Br-, I-, and NO3-, suggesting that BFUR is an ideal selective anion receptor for CO32- and SO42-. Additionally, energy decomposition analysis based on localized molecular orbital energy decomposition analysis (LMO-EDA) was performed; electronic properties and behaviors of the present systems were further discussed according to calculations on frontier molecular orbital, UV-vis spectra, total electrostatic potential, and visualized weak interaction regions. The present theoretical exploration of BFUR@X (X = F-, Cl-, Br-, I-, CO32-, NO3-, and SO42-) systems is fundamentally crucial to establish an anion recognition structure-property relationship upon combination of different noncovalent interactions, that is, double-dentate hydrogen bond and double-side anion-π interactions.

Computational study of the interaction between NO, NO+, and NO- with H2O.

In this computational study the interaction of NO., NO+, and NO- with H2O: [NO--H2O]., 1 ., [NO--H2O]+, 1 + , and [NO--H2O]-, 1 - was analysed. The optimized geometries indicate that the relative position of NO and H2O depends on the total charge: (ON.--H-OH), (NO---H-OH), and (ON+--OH2). Moreover, atomic spin density along with frontier molecular orbitals help to identify the preferred reduction or oxidation sites on the nitric oxide. Thus, quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and natural bond-bond polarizability (NBBP) methods aid to quantify the electron delocalization level between NO and H2O, 1 + > 1 . > 1 - , and show the predominantly ionic, and covalent character to inter-molecular, and intra-molecular chemical bonds, respectively. Furthermore, the natural bond orbital (NBO) and localized molecular orbital energy decomposition analysis (LMO-EDA) methods enable energy analyses of the interaction between NO and H2O in the complexes 1 ., 1 + , and 1 - . Where, the first method showed that the interaction between the natural bond orbitals in 1 - is more favorable, than in 1 + , and less in 1 ., however, the second method designates that the total interaction energy is lower for 1 + in relation to 1 - and 1 ., due mainly to the electrostatic component. As a final point, analysis of the electrostatic potential surfaces provides a clear and direct explanation for the relative position of the monomers. It also shows that the predominant Coulombic attraction between H2O and the charged NO+, and NO- compounds will be stronger in relation to the neutral NO.. Graphical abstract ᅟ.

A theoretical study of the strong interactions between carbon dioxide and OH+ and NH2 + products resulting from protonation of 1,2-dioxirane-3-one and 1,2-oxaziridine-3-one, respectively

In this work, we investigate the nature of the O–O and O–N interactions in protonated 1,2-dioxirane-3-one derivatives and protonated 1,2-oxaziridine-3-one derivatives, respectively. The quantum theory of atoms in molecules and the natural bond orbital (NBO) method in conjunction with the localized molecular orbital energy decomposition analysis (LMOEDA) have been used. LMOEDA and NBO analyses reveal that the O–O and O–N interactions exhibit characteristics of dative covalent bonds. In addition, the L(r) = −∇2 ρ(r) function reveals that the O–O and O–N interactions can be categorized as strong hole–lump interactions.

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium-Ion Battery Electrolytes.

Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li(+) with pure carbonates and ethylene carbonate (EC)-based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06-2X/6-311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li-ion solvation in carbonates and EC-based mixtures. A strong local tetrahedral order involving four carbonates around the Li(+) was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li(+) ion with carbonates are negative and suggested the ion-carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li(+) interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO-EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li(+) ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO-EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li-ion batteries, which complies with experiments and other theoretical results.

Structure, binding energy and chiral discrimination in oxathiirane homodimers

Oxathiirane (XHCSO) homodimers bonded by hydrogen bonds (HB) and chalcogen bonds (YB) were studied at the Møller-Plesset (MP2) computational level. Binding energies obtained at the Coupled-Cluster level up to the Complete Basis Set limit [CCSD(T)/CBS] indicate that HB complexes present stronger binding modes than the YB complexes. In terms of chiral discrimination energy, R,S complexes are favored over R,R complexes with the exceptions of SiCl3 and SiF3 derivatives. Natural Bond Orbital (NBO) results are in agreement with the interaction energies in the case of the HB complexes, but could not discriminate between R,R and R,S in the YB complexes. The lack of correlation between molecular electrostatic values on the 0.001a.u. and binding energies, in addition to the discrepancies between Atoms in Molecules (AIM) and NBO results may suggest that the electrostatics is not the dominant term in the interaction energy. This was corroborated by the Localized Molecular Orbital Energy Decomposition Analysis (LMOEDA) calculations which showed that the exchange and dispersion terms are the most important attractive components for all the complexes studied, contributing up to 50.6% and 42.5% to the total attractive forces respectively.

Theoretical investigation of the interactions between the π‐systems of molecular organic semiconductors and an analysis of the contributions of repulsion and electrostatics

A concept for the interactions between π‐systems is necessary to understand a number of phenomena in modern material sciences such as supramolecular properties and self‐assembly. In the present article, we investigate the intermolecular interaction energies between organic semiconductors with extended π‐systems using SAPT (symmetry‐adapted perturbation theory), LMO‐EDA (localized molecular orbital energy decomposition analysis), DFT‐D (density functional theory including dispersion corrections), and force‐field approaches. Both apolar organic molecules such as acenes and highly polarized π‐systems of merocyanines and squaraines were used to probe the influence of electrostatics on the shape of the potential energy surfaces (PES) governing the geometric structures of aggregates. Our results reveal that the shapes of the PESs result from variations in the short‐range, highly specific repulsion forces even for highly polar molecules. Using distributed quadrupoles, we show that it is nevertheless possible to mimic the intermolecular potentials with electrostatics. This is also possible with van‐der‐Waals potentials and a simple overlap‐based force‐field ansatz based on the overlap between p‐orbitals. © 2016 Wiley Periodicals, Inc.