| 
 NWChem 4.6 Functionality and Capabilities
NWChem provides many methods to compute the properties of molecular and
periodic systems using standard quantum mechanical descriptions of the
electronic wavefunction or density.  In addition, NWChem has the
capability to perform classical molecular dynamics and free energy
simulations.  These approaches may be combined to perform mixed
quantum-mechanics and molecular-mechanics simulations.
 
NWChem is available on almost all high performance computing platforms,
workstations, PCs running LINUX, as well as clusters of desktop platforms or
workgroup servers. NWChem development has been devoted to providing
maximum efficiency on massively parallel processors. It achieves this performance
on the 128 node Hewlett Packard Linux system in the EMSL's MSCF. It
has not been optimized for high performance on single processor desktop systems.
 
 
1. Molecular electronic structure
The following quantum mechanical methods are available to calculate
energies, analytic first derivatives and second derivatives with respect to atomic
coordinates.
 
 
Self Consistent Field (SCF) or Hartree Fock (RHF, UHF).Gaussian Density Functional Theory (DFT), using many local,
  non-local (gradient-corrected), and hybrid (local, non-local, and HF)
exchange-correlation potentials (spin-restricted)
with formal  and  scaling. 
The following methods are available to calculate energies and analytic
first derivatives with respect to atomic coordinates.  Second derivatives
are computed by finite difference of the first derivatives.
 
Self Consistent Field (SCF) or Hartree Fock (ROHF)Gaussian Density Functional Theory (DFT), using many local,
  non-local (gradient-corrected), and hybrid (local, non-local, and HF)
exchange-correlation potentials (spin-restricted)
with formal  and  scaling.Spin-orbit DFT (SODFT), using many local and non-local
  exchange-correlation potentials (UHF)MP2 including semi-direct using frozen core and RHF and UHF reference.Complete active space SCF (CASSCF) 
The following methods are available to compute energies only.  First
and second derivatives are computed by finite difference of the
energies.
 
CCSD, CCSD(T), CCSD+T(CCSD), with RHF referenceSelected-CI with second-order perturbation correctionMP2 fully-direct with RHF referenceResolution of the identity integral approximation MP2 (RI-MP2), with
  RHF and UHF reference. 
For all methods, the following operations may be performed:
 
Single point energyGeometry optimization (minimization and transition state)Molecular dynamics on the fully ab initio potential energy
  surfaceNumerical first and second derivatives automatically computed if
  analytic derivatives are not availableNormal mode vibrational analysis in cartesian coordinatesONIOM hybrid method of Morokuma and co-workersGeneration of the electron density file for graphical displayEvaluation of static, one-electron propertiesElectrostatic potential fit of atomic partial charges (CHELPG method with
    optional RESP restraints or charge constraints) 
For closed and open shell SCF and DFT:
 
COSMO energies - the continuum solvation 'Conductor-Like Screening' Model
    of A. Klamt and G. Schuurmann to describe dielectric screening effects in
    solvents. 
In addition, automatic interfaces are provided to
 
The natural bond orbital (NBO) packagePythonPOLYRATE, which is a program for the calculation of chemical reaction rates of polyatomic species (and also atoms and diatroms as special cases). 
 
2. Relativistic effects
The following methods for including relativity in quantum chemistry
calculations are available:
 
The spin-free one-electron Douglas-Kroll approximation is available for all
 quantum mechanical methods and their gradients.Dyall's spin-free Modified Dirac Hamiltonian approximation is available
 for the Hartree-Fock method and its gradients.One-electron spin-orbit effects can be included via spin-orbit potentials.
 This option is available for DFT and its gradients, but has to be run without
 symmetry. 
 
3. Pseudopotential plane-wave electronic structure
Two modules are available to compute the energy, optimize the
geometry, numerical second derivatives, and perform ab initio
molecular dynamics using pseudopotential plane-wave DFT.
 
 
PSPW - (Pseudopotential plane-wave) A gamma point code for calculating
molecules, liquids, crystals, and surfaces.Band - A prototype band structure code for calculating crystals and
surfaces with small band gaps (e.g. semi-conductors and metals) 
With
 
 
Conjugate gradient and limited memory BFGS minimizationCar-Parrinello (extended Lagrangian dynamics)Constant energy and constant temperature Car-Parrinello simulationsFixed atoms in cartesian and SHAKE constraints in Car-ParrinelloPseudopotential librariesHamann and Troullier-Martins norm-conserving pseudopotentials with
optional semicore correctionsAutomated wavefunction initial guess, now with LCAOVosko and PBE96 exchange-correlation potentials (spin-restricted
and unrestricted)Orthorhombic simulation cells with periodic and free space boundary conditions.Modules to convert between small and large plane-wave expansionsInterface to DRIVER, STEPPER, and VIB modulesPolarization through the use of point chargesMulliken, point charge, DPLOT (wavefunction, density and electrostatic
potential plotting) analysis 
4. Molecular dynamics
The following functionality is available for classical molecular
simulations:
 
Single configuration energy evaluationEnergy minimizationMolecular dynamics simulationFree energy simulation  (multistep thermodynamic perturbation (MSTP) or
    multiconfiguration thermodynamic integration (MCTI) methods with
    options of single and/or dual topologies, double wide sampling, and
    separation-shifted scaling) 
The classical force field includes:
 
Effective pair potentials (functional form used in AMBER, GROMOS,
    CHARMM, etc.) First order polarizationSelf consistent polarizationSmooth particle mesh Ewald (SPME) Twin range energy and force evaluation Periodic boundary conditionsSHAKE constraints Consistent temperature and/or pressure ensembles 
NWChem also has the capability to combine classical and quantum
descriptions in order to perform:
 
Mixed quantum-mechanics and molecular-mechanics (QM/MM)
  minimizations and molecular dynamics simulation , andQuantum molecular dynamics simulation by using any of the quantum
    mechanical methods capable of returning gradients. 
 
5. Python
The Python programming language has been embedded within NWChem and
many of the high level capabilities of NWChem can be easily combined
and controlled by the user to perform complex operations.
 
 
6. Parallel tools and libraries (ParSoft)
 
Global arrays (GA)Agregate Remote Memory Copy Interface (ARMCI)Linear Algebra (PeIGS) and FFTParIOMemory allocation (MA) 
 Updated: Wed. Sept. 10 17:16:21 PDT 2003
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