Calculation of Coulomb Interaction Parameters for La sub 2 CuO sub 4 Using a Constrained Density Functional Approach.

The constrained density functional approach is used to calculate the energy surface as a function of local charge fluctuations in La sub 2 CuO sub 4. This energy surface is then mapped onto a self consistent mean field solution of the Hubbard model which allows extraction of the Coulomb interaction parameters when combined with one-electron parameters derived from band structure results. Variations in local Cu d-charge and in plane O p-charge are considered for the prototypical high T sub c parent oxide La sub 2 CuO sub 4. To isolate the charge fluctuations the calculations are done in a supercell of size up to 2X2 in the basal plane. The local density functional calculations are done using the Linear Muffin Tin Orbital approach with the Atomic Sphere Approximation.