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.

First-principles prediction and partial characterization of the vibrational states of water up to dissociation

Abstract: A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H2 16O, the PES has a dissociation energy of D0 = 41 109 cm−1 and supports 1150 vibrational energy levels up to 41 083 cm−1. The deviation between the computed and the experimentally measured energy levels is below 15 cm−1 for all the states with energies less than 39 000 cm−1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm−1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.

Universality and chaoticity in ultracold K+KRb chemical reactions

Abstract: A fundamental question in the study of chemical reactions is how reactions proceed at a collision energy close to absolute zero. This question is no longer hypothetical: quantum degenerate gases of atoms and molecules can now be created at temperatures lower than a few tens of nanokelvin. Here we consider the benchmark ultracold reaction between, the most-celebrated ultracold molecule, KRb and K. We map out an accurate ab initio ground-state potential energy surface of the K2Rb complex in full dimensionality and report numerically-exact quantum-mechanical reaction dynamics. The distribution of rotationally resolved rates is shown to be Poissonian. An analysis of the hyperspherical adiabatic potential curves explains this statistical character revealing a chaotic distribution for the short-range collision complex that plays a key role in governing the reaction outcome.

Theoretical Study of the Ionization of Phenol−Water and Phenol−Ammonia Hydrogen-Bonded Complexes

Abstract: The ionization of phenol−water and phenol−ammonia complexes have been determined both using ab initio methods that include electron correlation and the hybrid three-parameter B3LYP density functional method The most stable structure of phenol−water cation corresponds to the C6H5OH+−H2O non-proton-transferred complex However, for the phenol−ammonia cation the calculations indicate that the only minimum on the potential energy surface corresponds to the C6H5O−NH4+ proton transferred form The computed B3LYP adiabatic ionization potentials for C6H5OH−H2O and C6H5OH−NH3 have been determined to be 765 and 733 eV, respectively The results obtained indicate that, for the neutral H-bonded systems, the B3LYP density functional method yields very similar results to those obtained with the ab initio MP2 or MCPF methods However, for the ionized radical cations, B3LYP results compare much better with experiment and to the MCPF method than UMP2 The unscaled B3LYP vibrational frequencies are in very good agreemen

Ab initio spectroscopy and photoinduced cooling of the trans-stilbene molecule

Abstract: We present a theoretical study of the S0→S1 and S0←S1 vibronic spectra for trans-stilbene. Franck–Condon spectra in the harmonic approximation are generated for the complete system with 72degrees of freedom by means of an analytic time-dependent approach accounting for Dushinsky rotations and thermal effects. The force fields are computed by means of density functional theory (DFT) and time-dependent DFT, on the one hand, and ab initio complete active space self-consistent field theory, on the other hand. The B3LYP functional shows that almost planar potential energy surface minima are found for the S0 and S1 state. Imposing C2h symmetry constraints, we obtain low-temperature high-resolution Franck–Condon spectra for both absorption and emission which are in reasonably good agreement with the experimental spectra measured by Syage et al. [J. Chem. Phys. 81, 4685 (1984)] in supersonic jets. Due to thermal population of low-energy modes, the room temperature absorption spectrum is very broad. An almost stru...

First principles computation of thermochemical properties beyond the harmonic approximation. I. Method and application to the water molecule and its isotopomers

Abstract: The anharmonic potential energy surface of water has been computed ab initio using an augmented coupled cluster method and various basis sets. Whereas the Pople 6–311 G family is manifestly unsatisfactory, Huzinaga–Dunning basis sets perform quite well. The [5s4p2d1f,3s2p] surface reproduces harmonic frequencies and anharmonicity constants to better than about 2 and 1 cm−1, respectively. For quantitative agreement with experiment, both f functions on oxygen and inclusion of core correlation seem to be prerequisite. Comparison with various experimentally derived force fields reveals that the ab initio force field is of comparable quality. From the best computed force field, a set of spectroscopic constants has been derived for all important isotopomers of water. Using a hybrid analytic/direct summation method recently developed by the present authors, the thermodynamic functions gef(T), hcf(T), S0, and Cp are computed including exact account of anharmonicity and rovibrational coupling, and very good analyt...