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Full-configuration interaction exactly solves the N-electron problem in a given 1-electron basis

Definitive molecular electronic structure Z. Gan and R.J. Harrison Computational Chemical Sciences Group Computer Science and Mathematics Division (harrisonrj@ornl.gov). Full-configuration interaction exactly solves the N-electron problem in a given 1-electron basis

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Full-configuration interaction exactly solves the N-electron problem in a given 1-electron basis

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  1. Definitive molecular electronic structure Z. Gan and R.J. HarrisonComputational Chemical Sciences GroupComputer Science and Mathematics Division(harrisonrj@ornl.gov) • Full-configuration interaction exactly solves the N-electron problem in a given 1-electron basis • It provides a critical benchmark for understanding and calibrating many-body calculations • Developed several new parallel-vector algorithms each of optimal for certain parameter values • Optimal algorithms for Cray differ sharply from those for IBM • The new code already enables computations 40+x larger and 100+x faster than previous work • 3.4 TFLOP/s sustained speed on 432 MSP (62% peak)

  2. Timing and performance results of FCI benchmark calculation of C2 ground state using 432 MSPs of Cray-X1a,b,c). a) C-C bond length takes the experimental value 1.2425 Å. The cc-pVTZ basis set, plus diffuse s (α=.04402) and p (α=.03569) functions, is employed. The FCI calculation involves 8 electrons in 68 orbitals, resulting 64,931,348,928 determinant space under D2h symmetry. b) FCI energy is computed based on RHF oribital. The 1s orbitals of carbon are frozen. The final FCI energy is -75.7854195035 Hartree. c) Maximum 432 MSPs could be requested under queue system. The sustained aggregated performance on 432MSPs exceeds 3.4Tflops, about 62% machine’s peak performance. d) Disk I/O is only performed once at the end of CI calculation, and it is not counted for the purpose of flop rate. For restarted calculations the CI vector on disk is read into memory as the initial guess.

  3. Parallel scalability of FCI Oxygen anion calculations on Cray-X1. Detailed Timing data of FCI Oxygen anion ground state calculation on Cray-X1a,b) • Aug-cc-pVQZ basis set was employed. FCI calculation is based on ROHF orbitals. • The 1s orbital is frozen in FCI calculation. The final FCI(7,79) calculation on Oxygen doublets includes 14,851,999,576 determinants in D2h symmetry.

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