 
Summary: HartreeFock solutions as a quasidiabatic basis for NonOrthogonal Configuration
Interaction
Alex J. W. Thom
Department of Chemistry, University of California Berkeley, California, 94720
Martin HeadGordon
Department of Chemistry, University of California Berkeley,
California, 94720 and Chemical Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, California, 94720
(Dated: September 30, 2009)
Using the method of SCF metadynamics, we locate some of the lowenergy solutions to the
HartreeFock (HF) equations on LiF and O3. The located solutions qualitatively resemble the adia
batic electronic states in these systems. We formulate the method of nonorthogonal Configuration
Interaction (CI) to interact these solutions, with cubic scaling with system size, and quadratic scal
ing with the number of solutions. The resultant solutions display the avoided crossings and, in O3,
a conical intersection expected of the adiabatic states. In LiF the relevant solutions coalesce and
disappear from Unrestricted HF space indicating a more general HF theory is required.
We have recently reported the method of Self
Consistent Field (SCF) Metadynamics[1] which enables
multiple solutions to the SCF equations (the stationary
values of the energy as a function of the electron density)
