Projected unrestricted Mo/ller–Plesset second-order energies and gradients
- 15 September 1990
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 93 (6) , 4123-4128
- https://doi.org/10.1063/1.458745
Abstract
The removal of spin contamination from unrestricted Hartree–Fock Mo/ller–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 n 2 v 3, 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.Keywords
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