Abstract
The authors present a new computational scheme to perform accurate and fast direct correlation-corrected vibrational self-consistent field (CC-VSCF) computations for a selected number of vibrational modes, which is aimed at predicting a few vibrations in large molecular systems. The method is based on a systematic selection of vibrational mode-mode coupling terms, leading to the direct ab initio construction of a sparse potential energy surface. The computational scaling of the CC-VSCF computation on the generated surface is then further reduced by using a screening procedure for the correlation-correction contributions. The proposed method is applied to the computation of the OH-stretch frequency of five aliphatic alcohols. The authors investigate the influence of different pseudopotential and all-electron basis sets on the quality of the correlated potential energy surfaces computed and on the OH-stretch frequencies calculated for each surface. With the help of these test systems, the authors show that their method offers a computational scaling that is two orders of magnitude lower than a standard CC-VSCF method and that it is of equal accuracy.
Highlights
One of the leading methodologies for computing accurate vibrational spectra of polyatomic molecules is the vibrational self-consistent fieldVSCFmethod developed by Carney et al.[1] and Bowman,[2] and its correlation-corrected extensionCC-VSCFby Norris et al.[3]
We describe in detail this new approach, named single-to-all CC-VSCFSTA-CC-VSCF, and use it to compute selected vibrational frequencies of a molecular system that are fully coupled to all other modes in the system, while the rest of the molecule is treated as a series of almost noncoupled anharmonic oscillators
Concerning the direct generation of MP2 potential energy surfaces, we observed that a set ofd, ppolarization functions is mandatory for pseudopotential basis sets when computing the OH-stretch frequency
Summary
One of the leading methodologies for computing accurate vibrational spectra of polyatomic molecules is the vibrational self-consistent fieldVSCFmethod developed by Carney et al.[1] and Bowman,[2] and its correlation-corrected extensionCC-VSCFby Norris et al.[3]. The VSCF wave function obtained is further refined using perturbation corrections This scheme has been implemented in a few ab initio programs,[4] allowing the calculation of the potential energy of the system using ab initio electronic structure theory while the CC-VSCF calculation is being performed. This direct CC-VSCF approach dispenses with the need to construct a functional form of the PES prior to solving the vibrational Schrödinger equation, and provides a direct route from the electronic structure to the vibrational spectrum of a molecule. This approach provides the full accuracy of a CC-VSCF treatment for the selected modes without the need to perform an elaborate computation for the less important modes in the system
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