Open-shell reduced density matrix functional theory

摘要

Open-shell reduced density matrix functional theory is established by investigating the domain ofnthe exact functional. For spin states that are the ground state, a particularly simple set is found tonbe the domain. It cannot be generalized to other spin states. A number of conditions satisfied bynthe exact density matrix functional is formulated and tested for approximate functionals. The exactnfunctional does not suffer from fractional spin error, which is the source of the static correlationnerror in dissociated molecules. We prove that a simple approximation (called the Buijse-Baerendsnfunctional, Müller or square root functional) has a non-positive fractional spin error. In the case ofnthe H atom the error is zero. Numerical results for a few atoms are given for approximate densitynand density matrix functionals as well as a recently developed range-separated combination of both.