Some basis ideas of the recent chemical Hamiltonian approach (CHA) are exposed without applying the somewhat involved second quantized formalism used previously. CHA permits avoidance of the explicit appearance of the three- and four-center integrals in the theory without neglecting them. (The "physical components" of the three- and four-center integrals are expressed as linear combinations of some one- and two-center integrals.) The absence of the three- and four-center integrals as independent entities reduces significantly the necessary computational work, conserving at the same time the fully ab initio character of the calculations; therefore CHA may represent a new paradigm in quantum chemistry (in particular SCF theory). The special equations which are necessary to apply the SCF method in the framework of CHA are derived, also without applying second quantization. They are somewhat more complicated than the usual HFR ones and lead to a non-Hermitean Fock matrix; the required orthonormalized MOs can however be found by a simple algorithm.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry