where {w i (r)} i=1,2 are trial Hückel-Slater molecular orbitals and {χ σ (i)} σ=±1 are spin functions. In above expression the microscopic parameters, U and K, are the magnitudes of intraatomic and interatomic Coulomb repulsion, respectively, t and V are the magnitudes of hopping (Bloch integral) and so-called cor-related hopping, respectively (for details see Methods) and