CRYSTAL2003 supports distributed memory parallelism in which the Fock, density and overlap matrices in k-space are distributed over the processors of the parallel machine. Direct SCF mode is used for mono-, bi-electronic and 3-centre (DFT potential integrals) in order to eliminate almost all I/O operations. This implementation is suitable for calculations using large numbers of nodes (>32) for low symmetry systems with 2000+ basis functions.

• ZSM5 B3LYP 621G* with 288 atoms/cell, 4416 atomic orbitals, 1 real k point, and no symmetry run for 2 SCF cycles (input file)

ZSM-5 cycle 1 elapsed times (s)

Machine	32	64	128	256
HPCx phase 2a	423.6	220.3	113.6	61.5
PPC970/Myrinet	422.1	234.9	131.4	93.3
Opteron-246/Ethernet	402.1	245.9	-	-
Opteron-246/SCI	355.6	221.8	-	-
Opteron-246/Infiniband	347.5	185.0	-	-
Opteron-280/SCORE	334.4	213.2	148.2	-
Opteron-280/SCOREx2	309.3	193.5	-	-
Opteron-248/Myrinet	301.9	189.3	127.9	-
Opteron-280/Infiniband	263.3	141.9	83.9	-