LAUSR

The mathematical underpinnings of a universal atomic-pair based approach to ab initio calculations of the electronic wave functions and energies of molecules and other atomic clusters are reported in non-relativistic Born-Oppenheimer approximation. The general approach utilizes the closure of an orthonormal (Eisenschitz-London) outer product of atomic spectral eigenstates to support totally antisymmetric aggregate eigenstates in the absence of explicit term-by-term atomic-product basis antisymmetry. Meaningful definitions of atomic-pair interaction operators and of their corresponding universal matrix representatives on the atomic product basis are obtained in this way for calculations on physical and chemical aggregates. Symmetric-group-based permutation-symmetry methods for partitioning of aggregate Hamlitonian matrices, performed to date by unitary transformations to remove unphysical “non-Pauli” states after aggregate Hamiltonian matrix construction, are supplemented here with a new two-step procedure...