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

Scalability of QM Code ASCI Research Review January 25, 1999

QM Methodology (Jaguar) Psuedospectral Technology (with Columbia U.) Multigrids Dealiasing functions Replace N 4 4-center Integrals with N 3 potentials Use Potentials to Form Euler-Lagrange Operator: CURRENT STATUS: Single processor speed 9 times faster than best alternate methodology Scales a factor of N 2 better than best alternate methodology 17 Log (number basis functions) Jaguar Gaussian CPU Time Collaboration with Columbia U. and Schrödinger Inc.

QM Scalability: IBM SP2

QM Scalability: SGI (Blue Mountain)

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  –Because H is a function of , 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

Improved Diagonalization Series of alkane chains, basis functions, bandwidth ~80 basis functions Band Diag: scales good (N 2.3 ) but overhead too high Normal Diag: scales poorly (N 3.3 ) but generally efficient Block Diag: scales best (<N 2 ) but generalization problems Fock Matrix

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

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/r 3 (dipole potential)

Divide, Conquer, and Recombine A B Eigenvalue Solving Going Up Already have eigs of H A and H B.  Make good guess at eigs of H (A+B) Can use fast (linear) diagonalization: Krylov-space Conjugate gradient Don’t have to do O(N 3 ) diagonalization

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  m 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 hr calculation! 10 nm 0.1  m HMX

MP Software Integration Issues ASCI Research Review January 25, 1999

Intra-MP Software Integration Issues Developing PUMP (Parallel Unified Materials Properties Interface) –Python-based framework to allow QM, MD, and  D 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. PUMP MD DD QM Properties Visualization Blue MountainASCI RedBlue Pacific CALTECH Computing Environment MSC & CACR

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

Extending Nitramine Reaction Pathways ASCI Research Review January 25, 1999

Additions to HE Reaction Kinetics GRI Nitromethane Mechanism –Right physics for small (C 2 NO 2 ) species, but no HMX, RDX, TATB Add in Yetter (Princeton) RDX Decomposition Pathways –Comb. Sci. Tech., 1997, 124, pp Determine analogous HMX Pathways Compute themochemical properties for all new species Final mechanism: –66 species –414 reactions

RDX Decomposition Steps

HMX Decomposition Steps

New Species Required in Mechanism RDX RDXR RDXRO HMX HMXR HMXRO

Fit NASA Parameters to QM Calculations Obtain thermochemistry from QM –Get QM structure at B3LYP/6-31G** level –Compute/scale frequencies –Obtain C p, S, H from K Fit to NASA standard form for thermochemical data:

Heat Capacity Fit

Entropy Fit

Enthalpy Fit

Testing the Mechanism CV Calculations –T = 1500 K –P = atm Species Profiles Induction Times

RDX/HMX Induction Times vs. Pressure

RDX Combustion, P = 1000 atm

HMX Combustion, P = 1000 atm

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