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<TITLE>4. Functionality</TITLE>
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HREF="node7.html">5. Top-level directives</A>
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<B> Previous:</B> <A NAME="tex2html1033"
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HREF="node5.html">3. NWChem Architecture</A>
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  <B> <A NAME="tex2html1041"
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HREF="node2.html">Contents</A></B>
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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
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<UL>
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<LI><A NAME="tex2html1044"
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HREF="node6.html#SECTION00610000000000000000">4.1 Molecular electronic structure</A>
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<LI><A NAME="tex2html1045"
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HREF="node6.html#SECTION00620000000000000000">4.2 Relativistic effects</A>
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<LI><A NAME="tex2html1046"
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HREF="node6.html#SECTION00630000000000000000">4.3 Pseudopotential plane-wave electronic structure</A>
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<LI><A NAME="tex2html1047"
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HREF="node6.html#SECTION00640000000000000000">4.4 Molecular dynamics</A>
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<LI><A NAME="tex2html1048"
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HREF="node6.html#SECTION00650000000000000000">4.5 Python</A>
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<LI><A NAME="tex2html1049"
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HREF="node6.html#SECTION00660000000000000000">4.6 Parallel tools and libraries (ParSoft)</A>
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</UL>
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<H1><A NAME="SECTION00600000000000000000">
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4. Functionality</A>
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</H1>
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<A NAME="sec:functionality"></A>
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<P>
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NWChem provides many methods to compute the properties of molecular and
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periodic systems using standard quantum mechanical descriptions of the
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electronic wavefunction or density. In addition, NWChem has the
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capability to perform classical molecular dynamics and free energy
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simulations. These approaches may be combined to perform mixed
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quantum-mechanics and molecular-mechanics simulations.
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<P>
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NWChem is available on almost all high performance computing platforms,
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workstations, PCs running LINUX, as well as clusters of desktop platforms or
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workgroup servers. NWChem development has been devoted to providing
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maximum efficiency on massively parallel processors. It achieves this performance
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on the 1960 processors HP Itanium2 system in the EMSL's MSCF.
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It has not been optimized for high performance on single processor desktop systems.
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<P>
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<H1><A NAME="SECTION00610000000000000000">
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4.1 Molecular electronic structure</A>
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</H1>
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<P>
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The following quantum mechanical methods are available to calculate
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energies, analytic first derivatives and second derivatives with respect to atomic
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coordinates.
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<P>
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<UL>
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<LI>Self Consistent Field (SCF) or Hartree Fock (RHF, UHF).
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</LI>
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<LI>Gaussian Density Functional Theory (DFT), using many local,
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non-local (gradient-corrected), and hybrid (local, non-local, and HF)
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exchange-correlation potentials
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(spin-restricted)
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with formal <IMG
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WIDTH="26" HEIGHT="16" ALIGN="BOTTOM" BORDER="0"
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SRC="img27.gif"
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ALT="$N^3$"> and <IMG
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WIDTH="26" HEIGHT="16" ALIGN="BOTTOM" BORDER="0"
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SRC="img28.gif"
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ALT="$N^4$"> scaling.
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</LI>
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</UL>
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<P>
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The following methods are available to calculate energies and analytic
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first derivatives with respect to atomic coordinates. Second derivatives
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are computed by finite difference of the first derivatives.
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<P>
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<UL>
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<LI>Self Consistent Field (SCF) or Hartree Fock (ROHF).
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</LI>
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<LI>Gaussian Density Functional Theory (DFT), using many local,
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non-local (gradient-corrected), and hybrid (local, non-local, and HF)
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exchange-correlation potentials
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(spin-unrestricted)
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with formal <IMG
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WIDTH="26" HEIGHT="16" ALIGN="BOTTOM" BORDER="0"
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SRC="img27.gif"
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ALT="$N^3$"> and <IMG
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WIDTH="26" HEIGHT="16" ALIGN="BOTTOM" BORDER="0"
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SRC="img28.gif"
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ALT="$N^4$"> scaling.
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</LI>
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<LI>Spin-orbit DFT (SODFT), using many local and non-local (gradient-corrected)
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exchange-correlation potentials (spin-unrestricted).
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</LI>
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<LI>MP2 including semi-direct using frozen core and RHF and UHF reference.
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</LI>
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<LI>Complete active space SCF (CASSCF).
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</LI>
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</UL>
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<P>
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The following methods are available to compute energies only. First
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and second derivatives are computed by finite difference of the
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energies.
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<UL>
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<LI>CCSD, CCSD(T), CCSD+T(CCSD), with RHF reference.
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</LI>
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<LI>Selected-CI with second-order perturbation correction.
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</LI>
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<LI>MP2 fully-direct with RHF reference.
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</LI>
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<LI>Resolution of the identity integral approximation MP2 (RI-MP2), with
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RHF and UHF reference.
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</LI>
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<LI>CIS, TDHF, TDDFT, and Tamm-Dancoff TDDFT for excited states with RHF, UHF, RDFT, or UDFT reference.
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</LI>
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<LI>CCSD(T) and CCSD[T] for closed- and open-shell systems (TCE module)
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</LI>
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<LI>UCCD, ULCCD, UCCSD, ULCCSD, UQCISD, UCCSDT, and UCCSDTQ with RHF, UHF, or ROHF reference.
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</LI>
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<LI>UCISD, UCISDT, and UCISDTQ with RHF, UHF, or ROHF reference.
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</LI>
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<LI>Non-canonical UMP2, UMP3, and UMP4 with RHF or UHF reference.
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</LI>
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<LI>EOM-CCSD, EOM-CCSDT, EOM-CCSDTQ for excitation energies, transition
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moments, and excited-state dipole moments of closed- and open-shell
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systems
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</LI>
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<LI>CCSD, CCSDT, CCSDTQ for dipole moments of closed- and open-shell
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systems
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</LI>
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</UL>
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<P>
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For all methods, the following operations may be performed:
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<UL>
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<LI>Single point energy
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</LI>
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<LI>Geometry optimization (minimization and transition state)
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</LI>
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<LI>Molecular dynamics on the fully <EM>ab initio</EM> potential energy
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surface
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</LI>
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<LI>Numerical first and second derivatives automatically computed if
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analytic derivatives are not available
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</LI>
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<LI>Normal mode vibrational analysis in cartesian coordinates
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</LI>
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<LI>ONIOM hybrid method of Morokuma and co-workers
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</LI>
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<LI>Generation of the electron density file for graphical display
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</LI>
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<LI>Evaluation of static, one-electron properties.
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</LI>
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<LI>Electrostatic potential fit of atomic partial charges (CHELPG method with
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optional RESP restraints or charge constraints)
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</LI>
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</UL>
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<P>
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For closed and open shell SCF and DFT:
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<UL>
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<LI>COSMO energies - the continuum solvation `COnductor-like Screening MOdel'
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of A. Klamt and G. Schüürmann to describe dielectric screening effects in
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solvents.
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</LI>
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</UL>
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<P>
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In addition, automatic interfaces are provided to
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<UL>
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<LI>The natural bond orbital (NBO) package
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</LI>
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<LI>Python
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</LI>
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</UL>
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<P>
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<H1><A NAME="SECTION00620000000000000000">
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4.2 Relativistic effects</A>
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</H1>
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<P>
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The following methods for including relativity in quantum chemistry
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calculations are available:
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<UL>
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<LI>The spin-free one-electron Douglas-Kroll approximation is available for all
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quantum mechanical methods and their gradients.
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</LI>
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<LI>Dyall's spin-free Modified Dirac Hamiltonian approximation is available
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for the Hartree-Fock method and its gradients.
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</LI>
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<LI>One-electron spin-orbit effects can be included via spin-orbit potentials.
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This option is available for DFT and its gradients, but has to be run without
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symmetry.
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</LI>
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</UL>
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<P>
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<H1><A NAME="SECTION00630000000000000000">
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4.3 Pseudopotential plane-wave electronic structure</A>
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</H1>
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<P>
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Two modules are available to compute the energy, optimize the
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geometry, numerical second derivatives, and perform ab initio
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molecular dynamics using pseudopotential plane-wave DFT.
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<P>
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<UL>
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<LI>PSPW - (Pseudopotential plane-wave) A gamma point code for calculating
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molecules, liquids, crystals, and surfaces.
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</LI>
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<LI>Band - A prototype band structure code for calculating crystals and
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surfaces with small band gaps (e.g. semi-conductors and metals)
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</LI>
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</UL>
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<P>
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With
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<P>
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<UL>
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<LI>Conjugate gradient and limited memory BFGS minimization
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</LI>
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<LI>Car-Parrinello (extended Lagrangian dynamics)
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</LI>
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<LI>Constant energy and constant temperature Car-Parrinello simulations
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</LI>
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<LI>Fixed atoms in cartesian and SHAKE constraints in Car-Parrinello
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</LI>
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<LI>Pseudopotential libraries
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</LI>
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<LI>Hamann and Troullier-Martins norm-conserving pseudopotentials with
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optional semicore corrections
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</LI>
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<LI>Automated wavefunction initial guess, now with LCAO
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</LI>
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<LI>Vosko and PBE96 exchange-correlation potentials (spin-restricted
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and unrestricted)
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</LI>
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<LI>Orthorhombic simulation cells with periodic and
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free space boundary conditions.
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</LI>
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<LI>Modules to convert between small and large plane-wave expansions
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</LI>
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<LI>Interface to DRIVER, STEPPER, and VIB modules
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</LI>
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<LI>Polarization through the use of point charges
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</LI>
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<LI>Mulliken, point charge, DPLOT (wavefunction, density and electrostatic
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potential plotting) analysis
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</LI>
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</UL>
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<P>
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<H1><A NAME="SECTION00640000000000000000">
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4.4 Molecular dynamics</A>
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</H1>
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<P>
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The following functionality is available for classical molecular
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simulations:
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<UL>
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<LI>Single configuration energy evaluation
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</LI>
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<LI>Energy minimization
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</LI>
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<LI>Molecular dynamics simulation
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</LI>
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<LI>Free energy simulation (multistep thermodynamic perturbation (MSTP) or
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multiconfiguration thermodynamic integration (MCTI) methods with
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options of single and/or dual topologies, double wide sampling, and
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separation-shifted scaling)
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</LI>
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</UL>
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<P>
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The classical force field includes:
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<UL>
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<LI>Effective pair potentials (functional form used in AMBER, GROMOS,
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CHARMM, etc.)
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</LI>
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<LI>First order polarization
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</LI>
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<LI>Self consistent polarization
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</LI>
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<LI>Smooth particle mesh Ewald (SPME)
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</LI>
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<LI>Twin range energy and force evaluation
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</LI>
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<LI>Periodic boundary conditions
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</LI>
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<LI>SHAKE constraints
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</LI>
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<LI>Consistent temperature and/or pressure ensembles
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</LI>
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</UL>
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<P>
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NWChem also has the capability to combine classical and quantum
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descriptions in order to perform:
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<UL>
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<LI>Mixed quantum-mechanics and molecular-mechanics (QM/MM)
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minimizations and molecular dynamics simulation , and
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</LI>
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<LI>Quantum molecular dynamics simulation by using any of the quantum
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mechanical methods capable of returning gradients.
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</LI>
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</UL>
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<P>
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By using the DIRDYVTST module of NWChem, the user can write an input
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file to the POLYRATE program, which can be used to calculate rate
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constants including quantum mechanical vibrational energies and tunneling
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contributions.
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<P>
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<H1><A NAME="SECTION00650000000000000000">
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4.5 Python</A>
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</H1>
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<P>
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The Python programming language has been embedded within NWChem and
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many of the high level capabilities of NWChem can be easily combined
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and controlled by the user to perform complex operations.
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<P>
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<H1><A NAME="SECTION00660000000000000000">
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4.6 Parallel tools and libraries (ParSoft)</A>
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</H1>
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<P>
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<UL>
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<LI>Global arrays (GA)
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</LI>
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<LI>Agregate Remote Memory Copy Interface (ARMCI)
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</LI>
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<LI>Linear Algebra (PeIGS) and FFT
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</LI>
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<LI>ParIO
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</LI>
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<LI>Memory allocation (MA)
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</LI>
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</UL>
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<P>
|
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<HR>
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<B> Previous:</B> <A NAME="tex2html1033"
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HREF="node2.html">Contents</A></B>
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Edoardo Apra
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2004-05-25
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