Reaction ergodography for the additions of HLi and its dimer to acetylene

The ab initio calculation has been performed with the addition pathways of HLi and its dimer to acetylene at the RHF/3-21G basis set. It shows that the reaction mechanisms of these two reactions are rather similar. In either of two reaction pathways, there is a meta-stable molecular complex near the isolated reactant state. This kind of addition can be treated approximately as the unimolecular reaction in which the molecular complex rearranges into the product. We have estimated the activation entropies and the statistical A factors of these two reactions by the use of RRKM theory. Frontier molecular orbital analysis of these two transition states reveals their HOMOS to be formed from both HOMO-LUMO and HOMO-HOMO interactions.     

Bonding of acetylene to copper atom,dimer, and trimer

The bonding of acetylene to copper atom, dimer, and trimer was investigated with a Kohn–Sham density functional approach. Full geometry optimization yielded the equilibrium structures of various Cu_nC₂H₂ species. Gradient corrections were included in the calculation of binding energies (BE ). The Cu—C₂H₂ complex was found to have a C_s structure and a BE of 10 kcal/mol. Three isomers of Cu₂C₂H₂ have similar total energies: a C_2v end-bonded structure with a BE of 18 kcal/mol, and two 1,2-dicupro ethylene isomers—a cis form with a BE of 12 kcal/mol and a trans form with a BE of 15 kcal/mol. Two stable C_2v isomers of Cu₃C₂H₂ were found. In both isomers, the Cu₃ ring relaxes from its isosceles structure, with two short bonds (2.247 Å) and one long bond (2.478 Å), and adopts a nearly equilateral geometry. In one isomer of Cu₃C₂H₂, the acetylene is bonded to one apex of the Cu₃ ring with a BE of 29 kcal/mol. In the other, it is bonded to two copper atoms of one side of the Cu₃ ring with a BE of 33 kcal/mol. © 1994 John Wiley & Sons, Inc.     

First principles NMR calculations by fragmentation

The nuclear magnetic shielding tensor is a molecular property that can be computed from first principles. In this work we show that by utilizing the fragmentation approach, one is able to accurately compute this property for a large class of molecules. This is of great significance because the computational expense required in the evaluation of the shielding tensor for all nuclei in a large molecule is now subject to near linear scaling. On the basis of previous studies and this work, it is also very likely that all molecular properties that can be expressed as derivatives of the total energy of the system are also amenable to accurate evaluation via fragmentation. If only the chemical shifts for nuclei in a small part of a large molecule are of interest, then only those molecular fragments containing those nuclei need to have their shielding tensors evaluated. Further, the fragmentation approach allows one to construct a database of molecular fragments that could, in principle, be used in the NMR characterization of molecules and at the same time provide possible three-dimensional representations of these molecules.     

First principles scheme to evaluate band edge positions in potential transition metal oxide photocatalysts and photoelectrodes

The positions of electronic band edges are one important metric for determining a material's capability to function in a solar energy conversion device that produces fuels from sunlight. In particular, the position of the valence band maximum (conduction band minimum) must lie lower (higher) in energy than the oxidation (reduction) reaction free energy in order for these reactions to be thermodynamically favorable. We present first principles quantum mechanics calculations of the band edge positions in five transition metal oxides and discuss the feasibility of using these materials in photoelectrochemical cells that produce fuels, including hydrogen, methane, methanol, and formic acid. The band gap center is determined within the framework of DFT+U theory. The valence band maximum (conduction band minimum) is found by subtracting (adding) half of the quasiparticle gap obtained from a non-self-consistent GW calculation. The calculations are validated against experimental data where possible; results for several materials including manganese(ii) oxide, iron(ii) oxide, iron(iii) oxide, copper(i) oxide and nickel(ii) oxide are presented.     

Model potential energy surfaces for approach of an electrophile to acetylene and fluoroacetylene

Non-empirical LCAO MO SCF calculations have been made on cross sections through prototype potential energy surfaces for the initial approach of an electrophile to acetylene and fluoroacetylene. The electrophile has been simulated by a unit positive charge and this is shown to give a computationally inexpensive means of providing information on such processes.     

Search for potential K ion battery cathodes by first principles

An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume change per K,and valence limit.With this screening method we predicted a series of potential K ions cathodes with favorable electrochemical performance,such as K₂VPO₄CO₃-like structures with 1 D diffusion channels,3 D channel structures K₂CoSiO₄,layered materials KCoO₂,KCrO₂,KVF₄ and K₅V₃F₁₄,and others.These potential cathodes have small volume changes,suitable voltage,and high capacity,with small diffusion barriers.They may be useful in K-ion batteries with high energy density and rate performance.     

Far-infrared band strengths in the water dimer: experiments and calculations

Most fundamentals modes of the water dimer have been experimentally determined, and the frequencies have been measured in either neon or parahydrogen matrices. The band strengths of all intramolecular and most intermolecular fundamentals of the water dimer have been measured. The results are further corroborated by comparison with the corresponding data for the fully deuterated water dimer. DFT calculations of the mode frequencies and band strength are in qualitative agreement with the experimental observations.     

Intermolecular potential energy surface for CS2 dimer

A new four‐dimensional intermolecular potential energy surface for CS₂ dimer is obtained by ab initio calculation of the interaction energies for a range of configurations and center‐of‐mass separation distances for the first time. The calculations were performed using the supermolecular approach at the Møller–Plesset second‐order perturbation (MP2) level of theory with the augmented correlation consistent basis sets (aug‐cc‐pVxZ, x = D, T) and corrected for the basis‐set superposition error using the full counterpoise correction method. A two‐point extrapolation method was used to extrapolate the calculated energy points to the complete basis set limit. The effect of using the higher levels of theory, quadratic configuration interaction containing single, double, and perturbative triple excitations QCISD(T) and coupled cluster singles, doubles and perturbative triples excitations CCSD(T), on the shape of potential energy surface was investigated. It is shown that the MP2 level of theory apparently performs extremely poorly for describing the intermolecular potential energy surface, overestimating the total energy by a factor of nearly 1.73 in comparison with the QCISD(T) and CCSD(T) values. The value of isotropic dipole–dipole dispersion coefficient (C₆) of CS₂ fluid was obtained from the extrapolated MP2 potential energy surface. The MP2 extrapolated energy points were fitted to well‐known analytical potential functions using two different methods to represent the potential energy surface analytically. The most stable configuration of the dimer was determined at R = 6.23 au, α = 90°, β = 90°, and γ = 90°, with a well depth of 3.980 kcal mol^?1 at the MP2 level of theory. Finally, the calculated second virial coefficients were compared with experimental values to test the quality of the presented potential energy surface. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011.     

Analytical fitting of potential energy surfaces for the Hxy systems

Use of the London-Eyring-Polanyi + 3-Center + power-series (LEP -3C -PS ) analytical potential as a fit to potential energy surfaces (PES ) which are known numerically only are suggested. This analytical fit was performed for the diatomics-in-molecules + 3 Center (DIM -3C ) PES of HCl₂ and HI₂ systems. The HCl₂ analytical LEP -3C-PS potential was used for classical trajectory calculations of the Cl' + HCl → HCl' + Cl reaction. The rate constant obtained from these calculations for T = 358° K is 1.95 X 10⁹ cm³/mol sec which is close to the experimental value of 2.5 10⁹ cm³/mol sec.     

On the fitting of analytical potential energy surfaces by constrained optimization

Analytical expressions for the He—H₂ potential energy surface have been obtained by non-linear constrained optimization techniques.     

Intermolecular potential and lattice dynamics of orthorhombic acetylene

The crystal structure and lattice dynamics of orthorhombic acetylene have been calculated with an intermolecular potential consisting of atom-atom and multipole-multipole interactions and including a hydrogen bond. A new assignment of the Raman lattice vibrations is discussed and utilized in the refinement of the potential parameters. The non-transferability of the potential to the cubic phase is attributed to the breaking of the hydrogen bond at the phase transition, and to the large anharmonicity expected for the high-temperature phase.     

Ab initio inter-radical potential for p-phenylenediamine radical cation dimer

Ab initio molecular orbital calculations were carried out to investigate the inter-radical interaction of the paired p-phenylenediamine radical cations in the singlet state. After initial optimization of the dimer in the parallel sandwich (D2h) and parallel displaced (Cs) configurations at the B3LYP/6-31G* theoretical level, the MP2/6-31G* and B3LYP/6-31G* single energies of the dimer were calculated as a function of the inter-radical distance R. The depths of the potential minima near R = 3.2 A were estimated to be in the order of the hydrogen bonding energy, assuming that the electrostatic contribution between the cations is canceled out by the attractive contributions due to the counter anions on the aspect of a simple electrostatic model. This can be related to the indications of the cation dimer formation in solution in the presence of counter anions at a low temperature reported previously in the literature by resonance Raman and electronic absorption spectra. The inter-radical (Raman active) frequencies of the dimer were calculated, one of which corresponds to the reported value at 161 cm(-1) observed in the resonance Raman spectrum in ethanol at 200 K by Yokoyama and Maeda (Chem. Phys. Lett. 48 (1977) 59).     

Intermolecular potential energy surface and second virial coefficients for the water-CO2 dimer

A five-dimensional potential energy surface is calculated for the interaction of water and CO(2), using second-order M?ller-Plesset perturbation theory and coupled-cluster theory with single, double, and perturbative triple excitations. The correlation energy component of the potential energy surface is corrected for basis set incompleteness. In agreement with previous studies, the most negative interaction energy is calculated for a structure with C(2v) symmetry, where the oxygen atom of water is close to the carbon atom of CO(2). Second virial coefficients for the water-CO(2) pair are calculated for a range of temperatures, and their uncertainties are estimated. The virial coefficients are shown to be in close agreement with the available experimental data.     

Electrostatic energy in the effective fragment potential method: theory and application to benzene dimer

Evaluation of the electrostatic energy within the effective fragment potential (EFP) method is presented. The performance of two variants of the distributed multipole analysis (DMA) together with two different models for estimating the charge penetration energies was studied using six homonuclear dimers. The importance of damping the higher order multipole terms, i.e. charge dipole, was also investigated. Damping corrections recover more than 70% of the charge penetration energy in all dimers, whereas higher order damping introduces only minor improvement. Electrostatic energies calculated by the numerical DMA are less accurate than those calculated by the analytic DMA. Analysis of bonding in the benzene dimer shows that EFP with inclusion of the electrostatic damping term performs very well compared to the high-level coupled cluster singles, doubles, and perturbative triples method. The largest error of 0.4 kcal/mol occurs for the sandwich dimer configuration. This error is about half the size of the corresponding error in second order perturbation theory. Thus, EFP in the current implementation is an accurate and computationally inexpensive method for calculating interaction energies in weakly bonded molecular complexes.     

First principles studies of SnTiO3 perovskite as potential environmentally benign ferroelectric material

In the context of the search for environment-respectful, lead- and bismuth-free chemical compounds for devices such as actuators, SnTiO₃ (ST) is investigated from first principles within DFT. Full geometry optimization provides a stable tetragonal structure relative to cubic one. From the equation of state the equilibrium volume of SnTiO₃ is found smaller than ferroelectric PbTiO₃ (PT) in agreement with a smaller Sn²⁺ radius. While ionic displacements exhibit similar trends between ST and PT, a larger tetragonality (c/a ratio) for ST results in a larger polarization, P_ST = 1.1 Cm⁻². Within ST analyzes of site projected density of states and chemical bonding indicate a reinforcement of the bond covalence with respect to Pb homologue. Both PT and ST exhibit anomalous large effective charges and the dielectric constant of ST is calculated larger than PT.     

First principles based mean field model for oxygen reduction reaction

A first principles-based mean field model was developed for the oxygen reduction reaction (ORR) taking account of the coverage- and material-dependent reversible potentials of the elementary steps. This model was applied to the simulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O(2) atmospheres. The results are consistent with those shown by past experimental and theoretical studies on surface coverages under Ar atmosphere, the shape of the current-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggests that the oxygen associative pathway including HO(2)(ads) formation is the main pathway on Pt(111), and that the rate determining step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloys and core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partial pressure of O(2)(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces the apparent reaction order with respect to the partial pressure to less than unity. This model shows details on how the reaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated.     

Interpolating moving least-squares methods for fitting potential energy surfaces: applications to classical dynamics calculations

As a continuation of our efforts to develop efficient and accurate interpolating moving least-squares (IMLS) methods for generating potential energy surfaces, we carry out classical trajectories and compute kinetics properties on higher degree IMLS surfaces. In this study, we have investigated the choice of coordinate system, the range of points (i.e., the cutoff radius) used in fitting, and strategies for selections of data points and basis elements. We illustrate and test the method by applying it to hydrogen peroxide (HOOH). In particular, reaction rates for the O-O bond breaking in HOOH are calculated on fitted surfaces using the classical trajectory approach to test the accuracy of the IMLS method for providing potentials for dynamics calculations.     

First principles determination of the bound levels of HeLi-

An analytical potential energy curve is developed from high quality ab initio calculations for the He+Li- interaction. The HeLi- electrostatic complex is found to have an Re of 18.5 bohrs and a De of 0.974 cm(-1). Numerical solution of the rovibrational Schr?dinger equation with this potential indicates two bound levels, (v,J)=(0,0) and (0,1), for all naturally occurring isotopologs (i.e., 4He7Li-, 4He6Li-, 3He7Li-, and 3He6Li-). For the common isotopolog, 4He7Li-, a D0 of 0.207 cm(-1) and an R0 of 26.5 bohrs is determined.     

Benzothiazinones by addition of o-Mercaptobenzamides to acetylene esters

The condensation of o-mercaptobenzamides with methyl acetylenedicarboxylate or methyl propiolate occurs with trans addition of the SH to the alkyne linkage. The resulting vinyl sulfide adducts can be ring closed to 1,3-benzothiazin-4-ones in excellent yield.