Ab initio study of the potential energy surface of CH4-H2O

Abstract

The potential energy surface of CH4-H2O is calculated through the fourth-order Mo/ller–Plesset perturbation theory. In an attempt to obtain basis-set saturated values of interaction energies the extended basis sets are augmented by bond functions which simulate the effects of high-symmetry polarization functions. The absolute minimum occurs for the configuration involving the C–H-O hydrogen-bond in which O-H points toward one of the faces of the CH4 tetrahedron. The equilibrium C–O separation is equal to 6.8 a0 which corresponds to the bond energy of 0.83 kcal/mol. Due to basis set unsaturation of the dispersion energy the bond energy may still be underestimated by about 0.05 kcal/mol. The secondary minimum involving the C-H–O hydrogen-bond is some 0.2 kcal/mol less stable, and the corresponding C–O distance is longer by 0.6 a0. The anisotropy of the potential energy surface is analyzed via the perturbation theory of intermolecular forces. The binding in CH4-H2O is chiefly due to the dispersion energy which sets the general trend for the anisotropy of the surface. A more detailed examination, however, indicates that the anisotropy of the surface results from a complex interplay of various factors, including electrostatics, exchange repulsion, and to a lesser degree, the deformation effects. Analysis of various exchangeless perturbation approximations to the deformation effect indicates that the neglect of exchange component of deformation may lead to an incorrect description of the van der Waals region. The analytical potential for the CH4-H2O interaction is provided.

Intermolecular charge transfer as evidence for unusual O–H⋯C(sp3) hydrogen bond

“…The analysis [65] of the PES for the methanewater complex with the use of the perturbation theory of intermolecular forces indicated the anisotropy, the feature that is believed to distinguish hydrogen bonds from van der Waals complexes. Some evidence for hydrogen bonding in the HOH ... CH 4 structure was obtained in the AIM theoretical study, which revealed a bond path connecting the hydrogen atom of water to the carbon of methane and corresponding (3, 1) bond critical point between these atoms [68].…”

Free Energy of the Hydrophobic Interaction from Molecular Dynamics Simulations: The Effects of Solute and Solvent Polarizability

“…Third, the Lennard-Jones parameters are chosen so that the minimum energy of the CH 4 -H 2 O dimer has a value and an oxygen carbon distance close to ab initio calculations at the fourthorder Møller-Plesset (MP4) level (Figure 1). 38 Figure 1 also…”

Four component regular relativistic Hamiltonians and the perturbational treatment of Dirac’s equation

“…After application of the BSSE correction, a planar structure in which H 2 lies on the C 2V axis was found to have lower energy. These calculations and also past studies 25,31,79 indicate that BSSE correction to the geometry is particularly important when an electrophilic species approaches the lone pair of oxygen.…”

“…[25][26][27][31][32][40][41][42][43]76. In this analysis the interaction energy is decomposed into components of different physical origins, such as electrostatic, dispersion, and exchange repulsion.…”

“…25,31,56 -60 It was found that the change in equilibrium distances after applying the counterpoise correction can be quite large. 57 Erroneous behavior of the BSSE-uncorrected potential energy surface ͑PES͒ was observed for several complexes involving the water molecule 25,31,59 and SCO. 60 One of the aims of this work is to show how the BSSE influences the equilibrium structure of the investigated systems.…”