The removal of spin contamination from unrestricted Hartree-Fock Møller-Plesset calculations is now recognized to be important. Here the Handy-Knowles formulation, previously presented, is studied. An evaluation of the energy and the energy gradient, for the removal of one- and two-spin contaminants, is described. The cost of the algorithm for the gradient is proportional to n2v3, where n and v are the number of occupied and virtual orbitals, respectively. Applications of this algorithm are presented for CN, Li3, and the abstraction of H from CH4. © 1990 American Institute of Physics.
CITATION STYLE
Handy, N. C., Su, M. D., Coffin, J., & Amos, R. D. (1990). Projected unrestricted Moller-Plesset second-order energies and gradients. The Journal of Chemical Physics, 93(6), 4123–4128. https://doi.org/10.1063/1.458745
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