Journal
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 14, Issue 3, Pages 1333-1350Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.7b01138
Keywords
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Funding
- Arnold and Mabel Beckman Foundation
- Department of Energy, Office of Basic Energy Sciences [DE-SC0015512, DE-FG02-07ER15884]
- Research Council of Norway through a Centre of Excellence Grant [179568, 262695]
- European Research Council [279619]
- U.S. Department of Energy (DOE) [DE-SC0015512] Funding Source: U.S. Department of Energy (DOE)
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Geometric energy derivatives which rely on core-corrected focal-point energies extrapolated to the complete basis set (CBS) limit of coupled cluster theory with iterative and noniterative quadruple excitations, CCSDTQ and CCSDT(Q), are used as elements of molecular gradients and, in the case of CCSDT(Q), expansion coefficients of an anharmonic force field. These gradients are used to determine the CCSDTQ/CBS and CCSDT(Q)/CBS equilibrium structure of the S-0 ground state of H2CO where excellent agreement is observed with previous work and experimentally derived results. A fourth-order expansion about this CCSDT(Q)/CBS reference geometry using the same level of theory produces an exceptional level of agreement to spectroscopically observed vibrational band origins with a MAE of 0.57 cm(-1). Second-order vibrational perturbation theory (VPT2) and variational discrete variable representation (DVR) results are contrasted and discussed. Vibration-rotation, anharmonicity, and centrifugal distortion constants from the VPT2 analysis are reported and compared to previous work. Additionally, an initial application of a sum-over-states fourth-order vibrational perturbation theory (VPT4) formalism is employed herein, utilizing quintic and sextic derivatives obtained with a recursive algorithmic approach for response theory.
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