Optimized coordinates in vibrational coupled cluster calculations

Abstract

Articles you may be interested inOrbitally invariant internally contracted multireference unitary coupled cluster theory and its perturbative approximation: Theory and test calculations of second order approximation J. Chem. Phys. 137, 014108 (2012); 10.1063/1.4731634 Accurate calculation of vibrational frequencies using explicitly correlated coupled-cluster theory Accurate calculation of anharmonic vibrational frequencies of medium sized molecules using local coupled cluster methods J. Chem. Phys. 126, 134108 (2007); 10.1063/1.2718951 MRCI calculations on the helium dimer employing an interaction optimized basis setThe use of variationally optimized coordinates, which minimize the vibrational self-consistent field (VSCF) ground state energy with respect to orthogonal transformations of the coordinates, has recently been shown to improve the convergence of vibrational configuration interaction (VCI) towards the exact full VCI [K. Yagi, M. Keçeli, and S. Hirata, J. Chem. Phys. 137, 204118 (2012)]. The present paper proposes an incorporation of optimized coordinates into the vibrational coupled cluster (VCC), which has in the past been shown to outperform VCI in approximate calculations where similar restricted state spaces are employed in VCI and VCC. An embarrassingly parallel algorithm for variational optimization of coordinates for VSCF is implemented and the resulting coordinates and potentials are introduced into a VCC program. The performance of VCC in optimized coordinates (denoted oc-VCC) is examined through pilot applications to water, formaldehyde, and a series of water clusters (dimer, trimer, and hexamer) by comparing the calculated vibrational energy levels with those of the conventional VCC in normal coordinates and VCI in optimized coordinates. For water clusters, in particular, oc-VCC is found to gain orders of magnitude improvement in the accuracy, exemplifying that the combination of optimized coordinates localized to each monomer with the size-extensive VCC wave function provides a supreme description of systems consisting of weakly interacting sub-systems.

Hybrid Optimized and Localized Vibrational Coordinates

“…The implementation builds completely on the existing MidasCpp implementation of OCs, see Ref. 9. The LC determination follows Jacob and Reiher 18 closely but with the distinction that the reported results in this paper are obtained from numerical calculations, while their rotation angles for LCs are obtained analytically.…”

“…The LC determination follows Jacob and Reiher 18 closely but with the distinction that the reported results in this paper are obtained from numerical calculations, while their rotation angles for LCs are obtained analytically. The implementation of the hybrid method allows the user to input the weights in an arbitrary way only constrained by the condition given in equation (9). All quantities in the hybrid measure are given in atomic units.…”

“…It is interesting to note that the localization of bending vibration coordinates we observe in the HOLCs improves the vibrational structure calculations in a manner that is comparable to localization of stretching vibrations, which have previously been found for OCs compared to NCs. 9 The localization of bending vibrations seems to be less important than the localization of stretching vibrations but not negligible in magnitude for vibrational structure calculations. This suggests that coordinate optimization methods that only take energy minimization into account might not always result in coordinate sets that are optimal in every possible regard.…”

“…Refs. 8,9,18. The rotation angle for each pair of coordinates at each iteration in this algorithm is chosen such that it brings the coordinates closer to the optimal ones with respect to the chosen optimization criteria.…”

The performance of RI-MP2 based potential energy surfaces in a vibrational self-consistent field treatment

“…This approach, being chosen for many applications due to its foreseeable computational cost and the promising results, is commonly abbreviated as second order perturbation theory augmented (PT2) VSCF or correlation-corrected (CC)-VSCF [8,22,23]. For cases where mode-mode correlations become large and where a mode-separated reference state might not suffice, techniques such as vibrational configuration interac-A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 tion (VCI) [24,25,26,27], vibrational multi-configurational self-consistent field (VMCSCF) [28,29] or vibrational coupled cluster (VCC) [30,31,32] have been established, representing today's state-of-the-art in anharmonic computational spectroscopy.…”