An efficient and numerically stable procedure for generating sextic force fields in normal mode coordinates
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In this paper, we outline a general, scalable, and black-box approach for calculating high-order strongly coupled force fields in rectilinear normal mode coordinates, based upon constructing low order expansions in curvilinear coordinates with naturally limited mode-mode coupling, and then transforming between coordinate sets analytically. The optimal balance between accuracy and efficiency is achieved by transforming from 3 mode representation quartic force fields in curvilinear normal mode coordinates to 4 mode representation sextic force fields in rectilinear normal modes. Using this reduced mode-representation strategy introduces an error of only 1 cm -1 in fundamental frequencies, on average, across a sizable test set of molecules. We demonstrate that if it is feasible to generate an initial semi-quartic force field in curvilinear normal mode coordinates from ab initio data, then the subsequent coordinate transformation procedure will be relatively fast with modest memory demands. This procedure facilitates solving the nuclear vibrational problem, as all required integrals can be evaluated analytically. Our coordinate transformation code is implemented within the ex tensible PyPES library program package, at http://sourceforge.net/projects/pypes-lib-ext/.
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03 Chemical Sciences
09 Engineering
Fields of Research::34 - Chemical sciences::3407 - Theoretical and computational chemistry::340701 - Computational chemistry
Fields of Research::34 - Chemical sciences::3401 - Analytical chemistry::340101 - Analytical spectrometry
Fields of Research::46 - Information and computing sciences::4601 - Applied computing::460104 - Applications in physical sciences
Fields of Research::51 - Physical sciences::5102 - Atomic, molecular and optical physics::510201 - Atomic and molecular physics
Fields of Research::34 - Chemical sciences::3407 - Theoretical and computational chemistry::340704 - Theoretical quantum chemistry