Very large-scale Very large-scale computations of the free computations of the free

energies ofenergies of eight low-lying eight low-lying structures of structures of argininearginine in the in the

gas phasegas phase

Robert J. GdanitzRobert J. Gdanitz

NC A&T State UniversityNC A&T State University

5 canonical (neutral) and 5 canonical (neutral) and 3 zwitterionic structures3 zwitterionic structures

C1 C2 C3 C4

C5 Z1 Z2 Z3

C1 C2

C3 C4

C5 Z1

Z2 Z3

TheoryTheory

Electronic SchrElectronic Schrödinger equationödinger equation::

Hamiltonian:Hamiltonian:

Constraint #2: Pauli principle:Constraint #2: Pauli principle:

Constraint #1: Spin symmetryConstraint #1: Spin symmetry

AlgebraizationAlgebraization

““Configuration Interaction” Configuration Interaction” (CI):(CI):

Slater determinants:Slater determinants:

Orbitals:Orbitals:

ApproximationApproximationBasisBasis setset

full-CIfull-CI

Approximation of full-CIApproximation of full-CI

Perturbation theory:Perturbation theory:

Coupled-Cluster:Coupled-Cluster:

Extrapolation to basis set limitExtrapolation to basis set limit

Independent particle contribution:Independent particle contribution:

Singlet pairs:Singlet pairs:

Triplet pairs:Triplet pairs:

Computers & Software Computers & Software (PNNL)(PNNL)

NWMpp1: 512-node IBM SP (retired)NWMpp1: 512-node IBM SP (retired)

NWMpp2: 1960-processor HP/LinuxNWMpp2: 1960-processor HP/Linux

NWChem, PNNLNWChem, PNNL

MP2/QZ and CCSD(T)/DZ:MP2/QZ and CCSD(T)/DZ:128 proc./48 GBytes of NWMpp1128 proc./48 GBytes of NWMpp1 for 2 daysfor 2 days

Energy w/r/t C5Energy w/r/t C5

-1

0

1

2

3

4

5

6

7

8

9

10

HF/DZ

~ TZ~ Q

Z

~ (DTQ)

HF/DZ + M

P2/DZ

~ TZ~ Q

Z

HF/TZ + MP2/(D

T)Z

HF/QZ + M

P2/(TQ)Z

HF/(DTQ)Z

+ MP2/(T

Q)Z

~ (x+1/2)-3

HF/(DTQ)Z

+ MP2/(T

Q)Z + C

CSD/DZ

~ + CCSD[T

]/DZ

~ CCSD(T

)/DZ

E [kcal/mol]

C1

C2

C3

C4

C5

Z1

Z2

Z3

The WinnersThe Winners

C3C3

CC55

G = 0.4 kcal/molG = 0.4 kcal/mol

ThanksThanks

Wim Cardoen, UtahWim Cardoen, Utah

Robert Harrison, Oak Ridge Nat’l LabRobert Harrison, Oak Ridge Nat’l Lab

Bert de Jong, PNNLBert de Jong, PNNL

Anita Orendt, UtahAnita Orendt, Utah

Jack Simons, Utah Jack Simons, Utah

Piotr Skurski, Gdansk, PolandPiotr Skurski, Gdansk, Poland

Theresa Windus, PNNLTheresa Windus, PNNL