Restricted ensemble Kohn-Sham

Restricted ensemble Kohn-Sham DFT Alternatively one can perform standard KS-DFT calculations on a collection of determinants with different occupations and take a weighted average of the individual energies to obtain an estimate of the mul-tideterminantal situation. To avoid the independent calculation of several KS determinants, a generalization of this approach was proposed by Filatov and Shaik based on the coupling operator technique developed by Roothaan for restricted open-shell Hartree-Fock. This restricted open-shell Kohn-Sham (ROKS) approach was later extended to situations where fractional occupation numbers are not imposed by the... 

M. Filatov and S. Shaik, Chem. Phys. Lett., 304, 429-437 (1999). A Spin-Restricted Ensemble-References Kohn-Sham Method and Its Application to Diradicaloid Situations. 

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