Virtual Test Facility: Materials Properties

1. Virtual Test Facility: Materials Properties ASCI Research Review January 25, 1999

2. Scalability of QM Code ASCI Research Review January 25, 1999

3. 17 • Psuedospectral Technology (with Columbia U.) • Multigrids • Dealiasing functions • Replace N4 4-center Integrals with N3 potentials • Use Potentials to Form Euler-Lagrange Operator: • CURRENT STATUS: • Single processor speed 9 times faster than best alternate methodology • Scales a factor of N2 better than best alternate methodology QM Methodology (Jaguar) Gaussian CPU Time Jaguar Log (number basis functions) Collaboration with Columbia U. and Schrödinger Inc.

4. QM Scalability: IBM SP2

5. QM Scalability: SGI (Blue Mountain)

6. QM Scalability: Comments • Clearly scaling needs work on Blue Mountain • Algorithm ill-suited to massive parallelizability • Seriel diagonalization • Local data • Two steps in Quantum Chemistry • Hamiltonian H formation • H diagonalization to produce density r • Because H is a function of r, this is a nonlinear problem • Linearization and parallelization in Quantum Chemistry requires techniques to localize the density. • Modified Divide-and-Conquer technique • Solves the H-formation and H-diagonalization problems • Generalize to metallic systems

7. Series of alkane chains, 276-552 basis functions, bandwidth ~80 basis functions Band Diag: scales good (N2.3) but overhead too high Normal Diag: scales poorly (N3.3) but generally efficient Block Diag: scales best (<N2) but generalization problems Improved Diagonalization Fock Matrix

8. nbf Divide and Conquer H Hamiltonian: Divided into fragments and buffer zones

9. Divide and Conquer Shortcomings • GOOD: • Solves H-formation, H-diagonalization, and parallelization simultaneously! • BAD if: Correlation lengths > fragment size! • Metals, surfaces, conjugated systems • Must hierarchically correct error in fragments • Pairwise recombination of fragments to yield larger fragments • Hierarchically combine larger fragments to yield still-larger fragments • Continue until converged • At each level, include additional H elements: • Few, since fall off as 1/r3 (dipole potential)

10. Divide, Conquer, and Recombine A B • Eigenvalue Solving Going Up • Already have eigs of HA and HB. • Make good guess at eigs of H(A+B) • Can use fast (linear) diagonalization: • Krylov-space • Conjugate gradient • Don’t have to do O(N3) diagonalization

11. Petaflop Dreaming • Tahir’s MD shock simulator with QM • 10,000,000 atoms on 1,000,000 processors  10 atoms/processor • depends upon ability to divide-and-conquer • simulate real chemistry: full species, bonds breaking, diffusion... • Shock wave travels 0.1 mm in 100 ps • time step ~1 fs  require 100,000 time steps • 1 time step takes 300 s • need 30,000,000 s = 10,000 hr = 1 year • Greatly simplify model using FF for unshocked region • Factor of 100 • 100 hr calculation! 10 nm HMX 10 nm 0.1 mm

12. MP Software Integration Issues ASCI Research Review January 25, 1999

13. Intra-MP Software Integration Issues • Developing PUMP (Parallel Unified Materials Properties Interface) • Python-based framework to allow QM, MD, and mD programs to transparently communicate. • Combine with simple OpenInventor-based graphics. • Combine with Thornley S-threads to allow load balancing on Intel shared memory boxes. • Combine with MPI to allow parallel execution. mD QM MD CALTECH Computing Environment MSC & CACR Visualization PUMP Properties Blue Mountain ASCI Red Blue Pacific

14. MP-Applications Integration Issues • Materials Property Database Under Construction • Need General Ways of Exchanging Complex Data • FF, EOS with HE • Reaction Mechanisms with HE • FF, EOS with SD/CT • Include in PUMP ability to write different archive formats • CVS archiving capabilities • Interface with Matlab/Python mathematical ability to derive data • XML-based web pages/publication of data

15. Extending Nitramine Reaction Pathways ASCI Research Review January 25, 1999

16. Additions to HE Reaction Kinetics • GRI Nitromethane Mechanism • Right physics for small (C2NO2) species, but no HMX, RDX, TATB • Add in Yetter (Princeton) RDX Decomposition Pathways • Comb. Sci. Tech., 1997, 124, pp. 25-82 • Determine analogous HMX Pathways • Compute themochemical properties for all new species • Final mechanism: • 66 species • 414 reactions

17. RDX Decomposition Steps

18. HMX Decomposition Steps

19. New Species Required in Mechanism HMX RDX HMXR RDXR HMXRO RDXRO

20. Fit NASA Parameters to QM Calculations • Obtain thermochemistry from QM • Get QM structure at B3LYP/6-31G** level • Compute/scale frequencies • Obtain Cp, S, H from 300 - 6300 K • Fit to NASA standard form for thermochemical data:

21. Heat Capacity Fit

22. Entropy Fit

23. Enthalpy Fit

24. Testing the Mechanism • CV Calculations • T = 1500 K • P = 1-100000 atm • Species Profiles • Induction Times

25. RDX/HMX Induction Times vs. Pressure

26. RDX Combustion, P = 1000 atm

27. HMX Combustion, P = 1000 atm

28. Next HE Steps... • TATB and PETN Decomposition Steps • F-containing species important in binder • Same fraction of F and Cl as binder • Explore reactions of intermediates