Semiclassical calculations of tunneling using interpolating moving least-squares potentials
Abstract
The interpolating moving least-squares (IMLS) and Local-IMLS methods are incorporated into semiclassical trajectory simulation. Issues related to the implementation are investigated. Potential energy surface (PES) constructed by the IMLS/L-IMLS methods is used to study tunneling in polyatomic systems HONO and malonaldehyde, where direct dynamics becomes prohibitively expensive at high ab initio levels. To study cis--trans isomerization in HONO, the PES is constructed by L-IMLS fitting at the MP4(SDQ)/6-31++G(d,p) level with the HDMR(5,3,3) basis set. Results obtained can be compared with the others in the literature. Semiclassical rates are close to the referenced quantum mechanical ones. The isomerization is governed by energy transfer into the reaction coordinate---the torsional mode; the rate is strongly mode-selective, and much faster for the cis--trans direction than for the opposite one. To study the ground-state splitting of malonaldehyde, the PES is first constructed by single-level L-IMLS fitting at the MP2/6-31G(d,p) level with the HDMR(3,2) basis set. The dual-level method is then employed for increasing accuracy of the PES and reducing computational cost using MP4/6-31G(d,p) as the high level method. Results obtained can be compared with the others in the literature. For 0.5 kcal/mol fitting tolerance the splitting is 38.7 and 8.8 cm-1 at MP2 single-level, and 29.6 and 5.5 cm-1 at MP4 dual-level for H9 and D5D9 isotopomers respectively, compared to the experiment of 21.6 and 2.884 cm-1 . Splitting is within two times of the experiment and agrees with other quantum mechanical and semiclassical studies.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 2012
- Bibcode:
- 2012PhDT.......243P
- Keywords:
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- Chemistry, Molecular;Engineering, Computer;Physics, Molecular