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.

Accurate determination of a potential energy surface for CD3H

Abstract: We present in this paper an application of the Lanczos algorithm to the fitting of a potential energy surface from the experimental spectrum. This method presents two definite improvements on the conventional approach: (i) the Lanczos algorithm allows to treat ultra‐large basis sets (120 000 states in this calculation) and (ii) it is possible to tune selectively the calculation to specific components of the spectrum (e.g., a given combination band nνi+mνj) thus reducing considerably the complexity of the fit. This method has been applied to the CD3H molecule, considering all the vibrational degrees of freedom. Converged line positions have been obtained for high overtones of the C–H stretching mode (up to 16 000 cm−1). The accuracy of the fitted surface is demonstrated by direct comparison of experimental and calculated spectroscopical parameters.

Improved computational strategy for the state‐selective coupled‐cluster theory with semi‐internal triexcited clusters: Potential energy surface of the HF molecule

Abstract: The recently developed state‐selective (SS) multi‐reference coupled‐cluster (CC) method involving all singly and doubly, and semi‐internal triply excited clusters from the formal reference configuration [SSCCSD(T) approach] is tested in the calculation of the potential energy surface (PES) of the HF molecule. Both double zeta and double zeta plus polarization basis sets are employed and a few different choices of active space are considered. The SSCCSD(T) method provides an accurate description of the entire PES at low cost even for the bond breaking region, contrary to the results obtained with the perturbative single‐reference CCSD(T) method or various limited configuration interaction approaches. This is the first application of the new SSCC code, which uses an improved computational strategy for handling the semi‐internal triexcited clusters. Details of this new implementation of the SSCCSD(T) method are discussed.

First principles simulation of the UV absorption spectrum of ethylene using the vertical Franck-Condon approach.

Abstract: A new method which we refer to as vertical Franck-Condon is proposed to calculate electronic absorption spectra of polyatomic molecules. In accord with the short-time picture of spectroscopy, the excited-state potential energy surface is expanded at the ground-state equilibrium geometry and the focus of the approach is more on the overall shape of the spectrum and the positions of the band maxima, rather than the precise position of the 0-0 lines. The Born-Oppenheimer approximation and the separability of the excited-state potential energy surface along the excited-state normal mode coordinates are assumed. However, the potential surface is not necessarily approximated as harmonic oscillator potentials along the individual normal modes. Instead, depending upon the nature of the potential surface along a particular normal mode, it is treated either in the harmonic approximation or the full one-dimensional potential is considered along this mode. The vertical Franck-Condon approach is applicable therefore even in cases where the excited state potential energy surface is highly anharmonic and the conventional harmonic Franck-Condon approach is inadequate. As an application of the method, the ultraviolet spectrum of ethylene between 6.2 eV ~50 000 cm 21 ! and 8.7 eV ~70 000 cm 21 ! is simulated, using the Similarity Transformed Equation of Motion Coupled-Cluster method to describe the required features of the potential energy surfaces. The spectrum is shown to be a result of sharp doublet structures stemming from the p!3s ~Rydberg! state superimposed on top of a broad band resulting from the p!p* ~valence! state. For the Rydberg state, the symmetric CvC stretch and the torsion mode contribute to the spectrum, while the broad valence band results from excitation into the CvC stretch, CH2 scissors, and the torsion mode. For both states, the potential along the torsion mode is highly anharmonic and the full treatment of the potential along this mode in the vertical Franck-Condon method is required. © 2004 American Institute of Physics. @DOI: 10.1063/1.1768173#

Interplay of Correlation and Relativistic Effects in Correlated Calculations on Transition-Metal Complexes: The (Cu2O2)(2+) Core Revisited.

Abstract: Owing to the availability of large-scale computing facilities and the development of efficient new algorithms, wave function-based ab initio calculations are becoming more common in bioinorganic chemistry. In principle they offer a systematic route toward high accuracy. However, these calculations are by no means trivial. In this contribution we address some pertinent points through a systematic theoretical study for the equilibrium between the peroxo- and bis-(μ-oxo) isomers of the [{Cu(C2H8N2)}2O2](2+) complex. While this system is often regarded as a prototypical multireference case, we treat it with the single reference local-pair natural orbital coupled cluster method and reiterate that the multireference character in this system is very limited. A set of intermediate structures, for the interconversion between the two isomers, is calculated through a relaxed surface scan thus allowing the calculation of an energetic profile that cleanly connects the bis-(μ-oxo) and side-on peroxo minima on the ground-state potential energy surface. Only at the highest level of theory involving complete basis set extrapolation, triple excitation contributions as well as relativistic and solvent effects, the bis-(μ-oxo) isomer is found to be slightly more stable than the peroxo structure. This is in agreement with the experimental findings. The effects of basis set, triples excitation, relativity, and solvent contribution have all been analyzed in detail. Finally, the ab initio results are compared with density functional calculations using various functionals. It is demonstrated that the largest part of the discrepancies of the results reported in the literature are due to an inconsistent handling of relativistic effects, which are large in both ab initio and density functional theory calculations.