We present an algorithm to estimate the anharmonic rovibrational density of states using Monte-Carlo integration of classical phase space. Numeric evaluation of the Jacobian allows the algorithm to make use of arbitrary curvilinear coordinate systems, which efficiently explore the space of molecular configurations. These coordinates allow the treatment of all internal degrees of freedom, including torsions. The algorithm also exploits the inherently parallel nature of Monte-Carlo integration to distribute computation across a large number of processors. The exactness and convergence properties of the algorithm are tested on CH4 using a model potential. A second test, involving C2H3, demonstrates the feasibility of direct sampling from an ab initio potential.

Calculation of anharmonic densities of states by classical phase space integrals

245th National Meeting (2013)

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