Configuration interaction singles method with multilayer fragment molecular orbital scheme

We have developed a parallelized integral-direct solver for configuration interaction singles (CIS) in the Abinit-mp program, by accepting the recently proposed multilayer fragment molecular orbital (MLFMO) method. In the MLFMO-CIS scheme, the region of interest in photoactive issues can be treated with the environmental potential at the Hartree-Fock (HF) level. The parallel efficiency is observed to be reasonable for the formaldehyde hydration system. A realistic applicability of the method is demonstrated for the photoactive yellow protein (PYP) including 125 amino acid residues.