NWChem is a computational chemistry package that is designed to run on high

performance
parallel supercomputers as well as conventional workstation clusters. It aims to be scalable both
in its ability to treat large problems efficiently, and in its us
age of available parallel computing
resources. NWChem has been developed by the Molecular Sciences Software group of the
Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National
Laboratory (PNNL). Most of the implementation has
been funded by the EMSL Construction
Project.
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
add
ition, 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 performan
ce 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.
1. Molecular e
lectronic 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 Dens
ity Functional Theory (DFT), using many local, non

local (gradient

corrected), and hybrid (local, non

local, and HF) exchange

correlation potentials (spin

restricted) with formal N
3
and N
4
scaling.
Wide range of supported exchange, correlation, and GGA fu
nctionals.
Click for the full
list.
The following methods are available to calculate energies and analytic first derivatives with
respect to atomic coordinates. Second de
rivatives 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) ex
change

correlation potentials (spin

unrestricted) with formal N
3
and N
4
scaling.
Spin

orbit DFT (SODFT), using many local and non

local (gradient

corrected) exchange

correlation potentials (spin

unrestricted).
MP2 including semi

direct using frozen core
and RHF and UHF reference.
Complete active space SCF (CASSCF).
Constrained DFT (CDFT)
DFT

D approach to add long

range dispersive corrections to DFT in an empirical fashion
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 reference.
Selected

CI with second

order perturbation correction.
MP2 fully

direct with RHF reference.
Resolution of the identity integral approximatio
n MP2 (RI

MP2), with RHF and UHF
reference.
CIS, TDHF, TDDFT, and Tamm

Dancoff TDDFT for excited states with RHF, UHF,
RDFT, or UDFT reference.
CCSD(T) and CCSD[T] for closed

and open

shell systems (TCE module)
UCCD, ULCCD, UCCSD, ULCCSD, UQCISD, UCCSD
T, and UCCSDTQ with RHF,
UHF, or ROHF reference.
UCISD, UCISDT, and UCISDTQ with RHF, UHF, or ROHF reference.
Non

canonical UMP2, UMP3, and UMP4 with RHF or UHF reference.
EOM

CCSD, EOM

CCSDT, EOM

CCSDTQ for excitation energies, transition
moments, and
excited

state dipole moments of closed

and open

shell systems
CCSD, CCSDT, CCSDTQ for dipole moments of closed

and open

shell systems
Second order approximate coupled

cluster model with singles and doubles (CC2) for
excited states in TCE
The following
methods can be used to calculate molecular properties:
Coupled

cluster linear response available using both restricted and unrestricted references
Ground

state dynamic polarizabilities at the CCSD and CCSDT levels of theory using the
linear response for
malism
Dynamic dipole polarizabilities at the CCSDTQ level using the linear response formalism
For all methods, the following operations may be performed:
Single point energy
Geometry optimization (minimization and transition state)
Molecular dynamics
on the fully
ab initio
potential energy surface
Numerical first and second derivatives automatically computed if analytic derivatives are
not available
Normal mode vibrational analysis in cartesian coordinates
ONIOM hybrid method of Morokuma and co

wor
kers
Generation of the electron density file for graphical display
Evaluation of static, one

electron properties.
Electrostatic potential fit of atomic partial charges (CHELPG method with optional RESP
restraints or charge constraints)
For closed and o
pen shell SCF and DFT:
COSMO energies

the continuum solvation `COnductor

like Screening MOdel' of A.
Klamt and G. Schüürmann to describe dielectric screening effects in solvents.
In addition, automatic interfaces are provided to
The natural bond orbit
al (NBO) package
Python
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 g
radients, but has to be run without symmetry.
Spin

free and spin

orbit zeroth

order relativistic approximation (ZORA) for DFT
3. Pseudopotential plane

wave electronic structure
Two modules are available to compute the energy, optimize the geometry, nume
rical 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 minimization
Car

Parrinello (extended Lagrangian dynamics)
Constant energy and constant temperature Car

Pa
rrinello simulations
Fixed atoms in cartesian and SHAKE constraints in Car

Parrinello
Pseudopotential libraries
Hamann and Troullier

Martins norm

conserving pseudopotentials with optional semicore
corrections
Automated wavefunction initial guess, now w
ith LCAO
Vosko 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 expansions
Interface to DR
IVER, STEPPER, and VIB modules
Polarization through the use of point charges
Mulliken, point charge, DPLOT (wavefunction, density and electrostatic potential
plotting) analysis
Fermi smearing added to BAND
Two

component wavefunctions added to BAND
HGH
spin

orbit potentials added to BAND
Hilbert decomposed parallel FFT added to BAND
Car

Parrinello QM/MM added to PSPW
Wannier orbital generation now works with non

cubic cells
New parallel decomposition in which both the FFT grid and orbitals are distr
ibuted has
been implemented in PSPW
Fractional occupation of molecular orbitals added to PSPW
2d processor grid for PSPW
Born

Oppenheimer dynamics option added to PSPW (i.e. task pspw Born

Oppenheimer)
4. Molecular dynamics
The following functionality
is available for classical molecular simulations:
Single configuration energy evaluation
Energy minimization
Molecular dynamics simulation
Free energy simulation (multistep thermodynamic perturbation (MSTP) or
multiconfiguration thermodynamic integrat
ion (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 polar
ization
Self consistent polarization
Smooth particle mesh Ewald (SPME)
Twin range energy and force evaluation
Periodic boundary conditions
SHAKE constraints
Consistent temperature and/or pressure ensembles
NWChem also has the capability to combine c
lassical and quantum descriptions in order to
perform:
Mixed quantum

mechanics and molecular

mechanics (QM/MM) minimizations and
molecular dynamics simulation , and
Quantum molecular dynamics simulation by using any of the quantum mechanical
methods capa
ble of returning gradients.
By using the DIRDYVTST module of NWChem, the user can write an input file to the
POLYRATE program, which can be used to calculate rate constants including quantum
mechanical vibrational energies and tunneling contributions.
5.
DNTMC
New Dynamical Nucleation Theory Monte Carlo (DNTMC) module to determine probability
distributions and evaporation rates of molecular clusters
6. Python
The Python programming language has been embedded within NWChem and many of the high
level cap
abilities of NWChem can be easily combined and controlled by the user to perform
complex operations.
7. Parallel tools and libraries (ParSoft)
Global arrays (GA)
Aggregate Remote Memory Copy Interface (ARMCI)
Linear Algebra (PeIGS) and FFT
ParIO
Memo
ry allocation (MA)
Home page:
http://www.emsl.pnl.gov/docs/nwchem/
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