A ONE-BILLION DETERMINANT FULL CI BENCHMARK ON THE CRAY-T3D

The implementation of an out-of-core version of a full CI algorithm on the Gray T3D is described. The introduction of heavy I/O activity, ne cessary to handle larger problems, required particular attention in or der to maintain good performance. As an application, the FCI energy of the Be, molecule with a [9s2p1d] basis set (all electrons), whose FCI space has a dimension of more than one billion (10(9)) of symmetry-ad apted determinants in D-2h symmetry was computed. A single iteration o n the Gray T3D at CINECA (64 processors) required about four hours, 30 minutes of which were spent in I/O operations. 27 iterations were per formed and a precision of at least one mu hartree in the energy was ac hieved. Due to the scalability of the code, substantially larger calcu lations could be performed provided that more processors and a larger amount of disk space were available.