Several variations of ab initio based molecular models for hydrogen fluoride ~HF! are examined by Monte Carlo molecular simulation to determine their bulk-phase properties. The models are taken from the literature, and represent fits of functional forms to the potential energy surface of the HF dimer as given by ab initio computational chemistry calculations. For one of these models, we examine...

A transferable potential energy function for describing the interaction between water molecules is presented. The electrostatic interaction is described rigorously using a multipole expansion. Only one expansion center is used per molecule to avoid the introduction of monopoles. This single center approach turns out to converge and give close agreement with ab initio calculations when carried o...

Nitromethane is a prototypical example for a molecule that can bind an extra electron in two fundamentally different ways forming dipole-bound as well as valence anions. The classification of the electronic states as dipole-bound or valence does in fact suggest a diabatic viewpoint, and we investigate the coupling between these two electronic states of the nitromethane anion. The coupling eleme...

In this study, we theoretically investigated Methyl hydrazinecarbodithioate by quantum chemical calculations for geometry optimization, vibration frequencies, and electronic structure parameters. The geometry optimization by DFT, ab initio MP2 method and the frequency calculation by DFT method was performed at the highest available Pople style 6-311G++(3df,3pd) basis set level. The semi-emp...

The competition between C-C and C-H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C-C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C-H insertion produced MC3H4 + H2. The measured product branching ratios verify the relati...

Ab initio calculations at the CCSD(T)/aug-cc-pVTZ level of theory were used to characterize the Ar-CH(3)OH intermolecular potential energy surface (PES). Potential energy curves were calculated for four different Ar + CH(3)OH orientations and used to derive an analytic function for the intermolecular PES. A sum of Ar-C, Ar-O, Ar-H(C), and Ar-H(O) two-body potentials gives an excellent fit to th...

Ab initio quantum chemical and free energy molecular dynamics calculations are performed to examine energy differences between the all-trans and (13,15)cis conformers of retinal, i.e., those populated in the dark-adapted state of bacteriorhodopsin. The quantum chemical results are used to derive an empirical force field that is used to calculate an adiabatic potential energy map for rotation ab...

The major factor determining the accuracy of ro-vibrational spectra of the water molecule is the accuracy of the Ž . underlying potential energy surface PES . We discuss improving the ab initio PES by introducing a correction to represent, accurately, the change in potential from equilibrium to linear geometries. We show the improvements which this has on calculated vibrational band origins and...