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.

An analytical six-dimensional potential energy surface for dissociation of molecular hydrogen on Cu(100)

Abstract: A six‐dimensional (6D) potential energy surface (PES) describing the molecule–surface interaction in the dissociative chemisorption system H2+Cu(100) is presented. The PES is based on slab calculations performed using the generalized gradient approximation (GGA) of density functional theory (DFT). To allow the use of the PES in dynamics calculations which can test the validity of the DFT/slab approach by comparing with available experiments on dissociative chemisorption, the PES was fit to an analytical form. The fit used describes the orientational dependence of the molecule–surface interaction above the high symmetry sites upto second order in spherical harmonics. The barriers to dissociation calculated for H2 approaching with its molecular axis parallel to the surface are all located in the exit channel. Also, for different impact sites and orientations, the height and the distance to the surface associated with the barrier correlate well with the chemisorption energy of the H‐atoms in the sites to whi...

Calculation of vibrational fundamental and overtone band intensities of h2o

Abstract: Vibrational intensities are calculated for the fundamental and overtone transitions of H2O up to approximately 18 000 cm−1. The intensities are determined from a dipole moment function expanded in the three internal bond coordinates. The expansion coefficients are computed ab initio at the second‐order Mo/ller–Plesset level of theory with a 6‐311G** basis set. Vibrational wave functions are calculated either from a three‐dimensional harmonically coupled anharmonic oscillator (HCAO) model which uses Morse oscillators to represent both the stretches and the bend of H2O, or from a variational calculation employing the best available potential energy surface and an exact kinetic energy operator. To obtain the most meaningful vibrational intensities we define dipole moment components using the Eckart embedding. Both the HCAO and the variational intensities agree quite well with the experimental results, which span eight orders of magnitude. From the calculations we predict that it may be possible to detect as yet unobserved vibrational transitions of H2O.

Rovibrational spectra of ammonia. I. Unprecedented accuracy of a potential energy surface used with nonadiabatic corrections.

Abstract: In this work, we build upon our previous work on the theoretical spectroscopy of ammonia, NH(3). Compared to our 2008 study, we include more physics in our rovibrational calculations and more experimental data in the refinement procedure, and these enable us to produce a potential energy surface (PES) of unprecedented accuracy. We call this the HSL-2 PES. The additional physics we include is a second-order correction for the breakdown of the Born-Oppenheimer approximation, and we find it to be critical for improved results. By including experimental data for higher rotational levels in the refinement procedure, we were able to greatly reduce our systematic errors for the rotational dependence of our predictions. These additions together lead to a significantly improved total angular momentum (J) dependence in our computed rovibrational energies. The root-mean-square error between our predictions using the HSL-2 PES and the reliable energy levels from the HITRAN database for J = 0-6 and J = 7∕8 for (14)NH(3) is only 0.015 cm(-1) and 0.020∕0.023 cm(-1), respectively. The root-mean-square errors for the characteristic inversion splittings are approximately 1∕3 smaller than those for energy levels. The root-mean-square error for the 6002 J = 0-8 transition energies is 0.020 cm(-1). Overall, for J = 0-8, the spectroscopic data computed with HSL-2 is roughly an order of magnitude more accurate relative to our previous best ammonia PES (denoted HSL-1). These impressive numbers are eclipsed only by the root-mean-square error between our predictions for purely rotational transition energies of (15)NH(3) and the highly accurate Cologne database (CDMS): 0.00034 cm(-1) (10 MHz), in other words, 2 orders of magnitude smaller. In addition, we identify a deficiency in the (15)NH(3) energy levels determined from a model of the experimental data.

Reactive and diffractive scattering of H-2 from Pt(111) studied using a six-dimensional wave packet method

Abstract: We present results of calculations on dissociative and rotationally (in)elastic diffractive scattering of H2 from Pt(111), treating all six molecular degrees of freedom quantum mechanically. The six-dimensional (6D) potential energy surface was taken from density functional theory calculations using the generalized gradient approximation and a slab representation of the metal surface. The 6D calculations show that out-of-plane diffraction is very efficient, at the cost of in-plane diffraction, as was the case in previous four-dimensional (4D) calculations. This could explain why so little in-plane diffraction was found in scattering experiments, suggesting the surface to be flat, whereas experiments on reaction suggested a corrugated surface. Results of calculations for off-normal incidence of (v=0,j=0) H2 show that initial parallel momentum inhibits dissociation at low normal translational energies, in agreement with experiment, but has little effect for higher energies. Reaction of initial (v=1,j=0) H2 ...