Q. Job terminates with “No memory left for SECI diagonalization”. I specified “MaxR2Op=100000000”.

 

A. This error message indicates the memory shortage at the SECI diagonalization step.  The reason would be in the option, "MaxR2Op=100000000".  This is too large.  A recommended value would be at most 500000.

In addition, you can use "RefCIWindow" option in the SAC-CI keyword.  This specifies the active orbitals in the SECI calculation. The SECI solution is used as the reference state for the perturbation selection of 2-electron excitation operators in the SAC-CI calculation. Therefore, the SECI active space is not necessarily equal to the SAC-CI active space.