English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

We present a perturbative method for ab initio calculations of rotational androvibrational effective Hamiltonians of both rigid and non-rigid molecules. Ourapproach is based on a curvilinear implementation of second order vibrationalM{\o}ller-Plesset perturbation theory (VMP2) extended to include rotationaleffects via a second order contact transformation. Though more expensive, thisapproach is significantly more accurate than standard second order vibrationalperturbation theory (VPT2) for systems that are poorly described to zerothorder by rectilinear normal mode harmonic oscillators. We apply this method anddemonstrate its accuracy on two molecules: Si$_2$C, a quasilinear triatomicwith significant bending anharmonicity, and CH$_3$NO$_2$, which contains acompletely unhindered methyl rotor. In addition to these two examples, wediscuss several key technical aspects of the method, including an efficientimplementation of Eckart and quasi-Eckart frame embedding that does not rely onnumerical finite differences.

journal of chemical physics online/the journal of chemical physics/journal of chemical physics

Ab initio effective rotational and rovibrational Hamiltonians for  non-rigid systems via curvilinear second order vibrational M{\o}ller-Plesset  perturbation theory