Mode-mode coupling map for the methanol molecule, representing the magnitude of the potential energy coupling for each pair of normal modes. The map is computed at the level of theory. Weaker couplings are represented by lighter-colored squares and stronger couplings by darker ones. Dots indicate the pair couplings included in a typical single-to-all calculation of the OH-stretch frequency (mode 1).
Representative timings for the vibrational part of the direct calculation of the OH-stretch vibrational frequency for aliphatic alcohols of varying carbon-chain length using the full CC-VSCF method, the single-to-all (STA) method without any CC screening (full CC), and the single-to-all method with CC screening (screened CC). All timings are relative to methanol at the full CC-VSCF level. The observed scaling was determined by linear regression of ln(time) vs , being the total number of normal modes in each system.
Comparison of the accuracy of the direct STA-CC-VSCF (STA) and the direct full CC-VSCF (Full) computation of the OH stretch for aliphatic alcohols of varying carbon-chain length using different levels of electronic structure theory. All frequencies are in .
Comparison of the direct STA-CC-VSCF vibrational frequencies of the OH stretch for methanol and ethanol using various potential energy surfaces. All frequencies are in . Differences from experimental values are given in parentheses.
Comparison of the direct STA-CC-VSCF vibrational frequencies of the OH stretch for aliphatic alcohols of different carbon-chain lengths. All frequencies are in .
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