On the accuracy of higher-order force constants calculated at the self-consistent field level of theory |
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| Affiliation: | 1. College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China;2. Research Institute of Geotechnical Engineering, Hohai University, Nanjing 210098, Jiangsu, China;3. Key Laboratory of Coastal Disaster and Defence, Ministry of Education, Hohai University, Nanjing, Jiangsu, 210098, China;4. Institute of Continuum Mechanics, Leibniz University Hannover, Hannover 30167, Germany;5. Department of Civil and Environmental Engineering, University of Waterloo, Ontario, N2L 3G1, Canada;6. Department of Computer Engineering, College of Computer and Information Sciences, King Saud University, Riyadh, Saudi Arabia |
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| Abstract: | ![]()
Cubic and quartic internal coordinate force constants are often obtained by a least-squares fit of a set of ab initio energies to an expansion of the potential energy. The reliability of such a procedure can now be determined, since analytic Cartesian cubic force constants are available which, when used in a finite difference procedure, also yield ab initio Cartesian quartic force constants. It is shown that unless the points of the energy grid are situated close to the equilibrium point unreliable results are obtained. This is why ab initio SCF anharmonic constants are more accurate than previously believed. |
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