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vibrational_perturbation_theory_vpt2 [2020/07/15 15:35]
qianli
vibrational_perturbation_theory_vpt2 [2020/07/15 15:36] (current)
qianli
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 ====== Vibrational perturbation theory (VPT2) ====== ====== Vibrational perturbation theory (VPT2) ======
  
-''VPT2'',//options// [vpt2]+''VPT2'',//options//
  
 The ''VPT2'' program is based on force constants, which are retrieved from the polynomial coefficients as generated by the ''POLY'' program. Therefore, each ''VPT2'' calculation requests a call of the ''POLY'' program prior to the ''VPT2'' call. As the ''VPT2'' program relies on a quartic force field (QFF), one may use the option ''TYPE=QFF'' in the ''SURF'' program. Once the ''XSURF'' program has been used, the directive ''%%VTAYLOR,TYPE=QFF%%'' should be called. This will lead to tremendous time savings as the size of the potential energy surface is significantly reduced. However, this is an option and the force constants can be retrieved from any potential provided by the ''SURF'' program. As the results may be sensitive to thresholds for the resonance treatment, the user may be careful concerning these. The current VPT2 implementation is limited to asymmetric top and linear molecules. For further details see:\\ The ''VPT2'' program is based on force constants, which are retrieved from the polynomial coefficients as generated by the ''POLY'' program. Therefore, each ''VPT2'' calculation requests a call of the ''POLY'' program prior to the ''VPT2'' call. As the ''VPT2'' program relies on a quartic force field (QFF), one may use the option ''TYPE=QFF'' in the ''SURF'' program. Once the ''XSURF'' program has been used, the directive ''%%VTAYLOR,TYPE=QFF%%'' should be called. This will lead to tremendous time savings as the size of the potential energy surface is significantly reduced. However, this is an option and the force constants can be retrieved from any potential provided by the ''SURF'' program. As the results may be sensitive to thresholds for the resonance treatment, the user may be careful concerning these. The current VPT2 implementation is limited to asymmetric top and linear molecules. For further details see:\\