Diagonalization-free initial guess to SCF calculations for large molecules

A new type of initial guess to iterative procedures of Hartree–Fock and density functional theory is suggested based on the adjustable density matrix assembler (ADMA) method [P.G. Mezey, J. Math. Chem. 18 (1995) 141]. The ADMA method approximates the density matrix based on a subdivision of molecules into fragments. This type of initial guess can be used in both the traditional SCF procedure and in density matrix iteration schemes such as suggested earlier [D. Köhalmi, Á. Szabados, P.R. Surján, Phys. Rev. Lett. 95 (2005) 013002]. The ADMA guess is especially important in the latter case, in which no matrix diagonalization is involved during the SCF cycle.