Semidirect algorithms for third‐order electron propagator calculations

An efficient procedure for third‐order electron propagator calculations of ionization energies and electron affinities is reported. Diagonal self‐energy expressions that are suitable for large molecules are empolyed. The outer‐valence Green's function method also is implemented. An integral transformation program for direct and semidirect algorithms is modified to store only nonzero integrals according to Abelian point group symmetry. Contributions to self‐energy matrix elements that depend on electron repulsion integrals with four virtual orbital indices are computed in a direct way. Intermediate batches of integrals are created by sort procedures while avoiding storage of transformed integrals in the main memory. This method permits calculation of electron binding energies for C   7 2−with a 231 atomic orbital basis and for Zn(C 5 H 5 ) 2 with a 220 atomic orbital basis on an IBM RISC/6000 Model 550. During these calculations, the CPU is engaged approximately 90% of the time. © 1995 John Wiley & Sons, Inc.