Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

Interaction potential between two rigid HF molecules

Abstract: As a prelude to the study of energy transfer in the HF–HF system, the potential energy surface for the interaction of two rigid HF molecules has been calculated within the ab initio self‐consistent‐field framework. An H(4s 1p/2s 1p), F(9s 5p 1d/4s 2p 1d) basis set of contracted Gaussian function was employed. The number of unique points on the surface is greatly reduced by symmetry, and only 294 points were required to give a fairly complete description of the four‐dimensional surface. Parts of the surface are illustrated by a series of contour maps. Some preliminary attempts to fit the surface to an analytic form are described. The equilibrium geometry of (HF)2 is predicted.

Collisions of excited Na atoms with H2 molecules. I. Ab initio potential energy surfaces and qualitative discussion of the quenching process

Abstract: Potential energy surfaces have been calculated for the four lowest electronic states of Na (3 2S, 3 2P)+H2(1Σ+g) by means of the RHF–SCF and PNO–CEPA methods. For the so‐called quenching process of Na (3 2P) by H2 at low initial translational energies (E–VRT energy transfer) the energetically most favorable path occurs in C2v symmetry, since—at intermediate Na–H2 separation—the ? 2B2 potential energy surface is attractive. From the CEPA calculations, the crossing point of minimal energy between the ? 2A1 and ? 2B2 surfaces is obtained at Rc = 3.57 a.u. and rc = 2.17 a.u. with an energy difference to the asymptotic limit (R = ∞, r = re) of −0.06 eV. It is thus classically accessible without any initial translational energy, but at low initial translational energies (∼0.1 eV) quenching will be efficient only for arrangements of collision partners close to C2v symmetry. There is little indication of an avoiding crossing with an ionic intermediate correlating asymptotically with Na+ and H2− as was assumed in ...

Water dimers in the atmosphere III: equilibrium constant from a flexible potential.

Abstract: We present new results for the water dimer equilibrium constant Kp(T) in the range 190−390 K, using a flexible potential energy surface fitted to spectroscopical data. The increased numerical complexity due to explicit consideration of the monomer vibrations is handled via an adiabatic (6 + 6)d decoupling between intra- and intermolecular modes. The convergence of the canonical partition function of the dimer is ensured by computing all energy levels up to dissociation for total angular momentum values J = 0−5 and using an extrapolation scheme to higher values. The newly calculated values for Kp(T) are in very good agreement with available experimental data at room temperature. At higher temperatures, an analysis of the convergence of the partition function reveals that quasi-bound states are likely to contribute to the equilibrium constant. Additional thermodynamical quantities (ΔG, ΔH, ΔS, and Cp) have also been determined and fit to quadratic expressions a + bT + cT2.

High level ab initio and density functional theory studies on methanol–water dimers and cyclic methanol(water)2 trimer

Abstract: The methanol-water dimers and the potential energy surface of the cyclic methanol(water)2 trimer have been studied through the use of high-level ab initio calculations and density functional methods. The geometries have been optimized at the MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory. The harmonic vibrational frequencies were obtained at the latter level. The final energies of the different local minima were calculated in the framework of the G2 and G2(MP2) theories. These values were compared with those obtained using the B3LYP/6-311+G(3df,2p) approach. At all the levels of theory considered the most stable conformer of methanol-water heterodimers corresponds to that in which water behaves as a hydrogen bond donor, in agreement with the most recent experimental evidences [P. A. Stockman et al., J. Chem. Phys. 107, 3782 (1997)]. The energy differences between the different conformers of the cyclic methanol(water)2 trimer are rather small, as well as the energy barriers connecting them. The g...