NWChem User Documentation Release 4.0.1 High Performance Computational Chemistry Group W.R. Wiley Environmental Molecular Sciences Laboratory Pacific Northwest National Laboratory P.O. Box 999, Richland, WA 99352 January 2001 2 DISCLAIMER This material was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the United States Department of Energy, nor Battelle, nor any of their employees, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY LEGAL LIABILITY OR RESPON- SIBILITY FOR THE ACCURACY, COMPLETENESS, OR USEFULNESS OF ANY INFORMATION, APPARA- TUS, PRODUCT, SOFTWARE, OR PROCESS DISCLOSED, OR REPRESENTS THAT ITS USE WOULD NOT INFRINGE PRIVATELY OWNED RIGHTS. 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Contents 1 Introduction 17 1.1 Citation . 17 1.2 User Feedback . 18 2 Getting Started 19 2.1 Input File Structure . 19 2.2 Simple Input File — SCF geometry optimization . 20 2.3 Water Molecule Sample Input File . 21 2.4 Input Format and Syntax for Directives . 23 2.4.1 Input Format . 23 2.4.2 Format and syntax of directives . 24 3 NWChem Architecture 27 3.1 Database Structure . 27 3.2 Persistence of data and restart . 29 4 Functionality 31 4.1 Molecular electronic structure . 31 4.2 Relativistic effects . 32 4.3 Pseudopotential plane-wave electronic structure . 33 4.4 Periodic system electronic structure . 33 4.5 Molecular dynamics . 33 4.6 Python . 34 4.7 Parallel tools and libraries (ParSoft) . 34 5 Top-level directives 35 5.1 START and RESTART — Start-up mode . 35 5 6 CONTENTS 5.2 SCRATCH_DIR and PERMANENT_DIR — File directories . 36 5.3 MEMORY — Control of memory limits . 38 5.4 ECHO — Print input file . 39 5.5 TITLE — Specify job title . 40 5.6 PRINT and NOPRINT — Print control . 40 5.7 SET — Enter data in the RTDB . 41 5.8 UNSET — Delete data in the RTDB . 43 5.9 STOP — Terminate processing . 43 5.10 TASK — Perform a task . 44 5.10.1 TASK Directive for Electronic Structure Calculations . 44 5.10.2 TASK Directive for Special Operations . 45 5.10.3 TASK Directive for the Bourne Shell . 46 5.10.4 TASK Directive for QM/MM simulations . 47 5.11 CHARGE — Total system charge . 47 6 Geometries 49 6.1 Keywords on the GEOMETRY directive . 50 6.2 Symmetry Group Input . 52 6.3 Cartesian coordinate input . 53 6.4 Z-matrix input . 54 6.5 ZCOORD — Forcing internal coordinates . 59 6.6 Applying constraints in geometry optimizations . 60 6.7 SYSTEM — Lattice parameters for periodic systems . 61 7 Basis sets 63 7.1 Basis set library . 64 7.2 Explicit basis set definition . 65 8 Effective Core Potentials 67 8.1 Scalar ECPs . 68 8.2 Spin-orbit ECPs . 70 9 Relativistic All-electron Approximations 71 9.1 Douglas-Kroll approximation . 72 9.2 Dyall’s Modified Dirac Hamitonian approximation . 72 CONTENTS 7 10 Hartree-Fock or Self-consistent Field 77 10.1 Wavefunction type . 77 10.2 SYM — use of symmetry . 78 10.3 ADAPT – symmetry adaptation of MOs . 78 10.4 TOL2E — integral screening threshold . 79 10.5 VECTORS — input/output of MO vectors . 79 10.5.1 Superposition of fragment molecular orbitals . 81 10.5.2 Atomic guess orbitals with charged atoms . 86 10.6 Accuracy of initial guess . 87 10.7 THRESH — convergence threshold . 87 10.8 MAXITER — iteration limit . 88 10.9 RI-SCF — resolution of the identity approximation . 88 10.10PROFILE — performance profile . 89 10.11DIIS — DIIS convergence . 89 10.12DIRECT and SEMIDIRECT — recomputation of integrals . 90 10.12.1 Integral File Size and Format for the SCF Module . 91 10.13SCF Convergence Control Options . 92 10.14NR — controlling the Newton-Raphson . 93 10.15LEVEL — level-shifting the orbital Hessian . 93 10.16Orbtial Localization . 94 10.17Printing Information from the SCF Module . 96 10.18Hartree-Fock or SCF, MCSCF and MP2 Gradients . 97 11 DFT for Molecules (DFT) 99 11.1 Specification of Basis Sets for the DFT Module . 101 11.2 VECTORS and MAX_OVL — KS-MO Vectors . 102 11.3 XC and DECOMP — Exchange-Correlation Potentials . 102 11.3.1 Optional Exchange Functionals . 103 11.3.2 Optional Correlation Functionals . 104 11.3.3 Combined Exchange and Correlation Functionals . 105 11.4 ITERATIONS — Number of SCF iterations . 108 11.5 CONVERGENCE — SCF Convergence Control . 108 11.6 GRID — Numerical Integration of the XC Potential . ..