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 usage 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.

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Nov 7, 2013 (4 years and 1 day ago)

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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/