ELECTRONIC STRUCTURE COMPUTATIONS OF VERY LARGE NONPERIODIC ATOMIC SYSTEMS ON CRAY PVP AND MPP ARCHITECTURES

A program for electronic structure computations, which scales linearly (O(N)) with the number of atoms in a system, has been implemented on a parallel-vector CRAY C90. The method is suitable for disordered systems, transition metal oxides, inter­ faces, superlattices, extended surface defects such as steps, microfacets and islands, and in general for nanometer-scale engineered structures consisting of millions of atoms. The program runs at a speed of 8.5 GFLOP/s on a 16-CPU CRAY C90. We believe that the computation performed using this program (1,105,920 atoms of rutile Ti02) is the largest quantum-mechanical electronic structure calculation reported so far. We report on our experiences of porting and optimizing this code on C90 and T3D architectures