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Periodic boundary conditions
It would be a good idea to add periodic boundary conditions calculations in Firefly. Not crystal calculations but periodic boundary conditions calculations with an atomic-like basis set as it is implemented for example in MOPAC. My experience with MOPAC shows that for organic molecular crystals, inorganic semiconductors, and even for some semimetals like arsenic the geometry obtained by PM6 Hamiltonian is quantitatively correct, and the errors are not due to the Gamma-point-only calculations but mainly due to the accuracy limitations of PM6 parametrization. By the way, Gaussian allows for periodic boundary conditions calculations and even crystal calculations with GTO basis set but for organic molecular crystals having typically more than 50 atoms in the unit cell (e.g. benzene) I am not able to obtain physically reasonable results.
Thu Aug 25 '11 4:44pm
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