Difference between revisions of "NWChem"
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| + | When in doubt, check the [http://www.nwchem-sw.org/index.php/Release62:NWChem_Documentation Documentation], and test! |
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| + | |||
| + | == Energy Calculation == |
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| + | |||
A simple SCF energy calculation on the input file '''start.xyz''' can be done with: |
A simple SCF energy calculation on the input file '''start.xyz''' can be done with: |
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task scf energy |
task scf energy |
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| + | == Geometry Optimization == |
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Running a geometry optimization just requires replacing the '''task''' directive. Here, we've also added a block of parameters controlling the minimization algorithm. |
Running a geometry optimization just requires replacing the '''task''' directive. Here, we've also added a block of parameters controlling the minimization algorithm. |
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loose |
loose |
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maxiter 150 |
maxiter 150 |
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| + | xyz opt |
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end |
end |
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task scf optimize |
task scf optimize |
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| + | |||
| + | == DFT == |
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You can also use DFT rather than HF (SCF) by changing the appropriate keywords and adding a DFT block to specify its functional: |
You can also use DFT rather than HF (SCF) by changing the appropriate keywords and adding a DFT block to specify its functional: |
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loose |
loose |
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maxiter 150 |
maxiter 150 |
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| + | xyz opt |
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end |
end |
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task dft optimize |
task dft optimize |
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| + | The "xyz opt" causes NWChem to write out coordinate files, e.g. '''opt-001.xyz''', ... as the optimization is proceeding. |
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| + | |||
| + | == Specifying Charge and Spin == |
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Of course, we need to be able to specify the charge and total spin for most systems as well. Here's an input example appropriate for Fe3+ (5 spin-up electrons making up a half-filled d-shell): |
Of course, we need to be able to specify the charge and total spin for most systems as well. Here's an input example appropriate for Fe3+ (5 spin-up electrons making up a half-filled d-shell): |
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task scf energy |
task scf energy |
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| + | == Vibrational Frequencies == |
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| + | |||
| + | At a minimum, the second derivatives of the potential energy surface with respect to the nuclear coordinates make up a 3Nx3N matrix. The eigenvectors represent vibrational 'modes,' and the eigenvalues represent their force constants. Analyzing each mode as a harmonic oscillator leads to a set of vibrational frequencies, which give thermochemical information on the molecule as well as IR spectroscopic information. |
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| + | |||
| + | From a minimized set of coordinates, all you should require is to add the appropriate task (and optionally a block of parameters) |
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| + | |||
| + | task scf frequencies |
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Revision as of 11:02, 4 November 2013
When in doubt, check the Documentation, and test!
Contents
Energy Calculation
A simple SCF energy calculation on the input file start.xyz can be done with:
start en_scf title "Pople SCF energy" geometry units angstrom load start.xyz end basis # * library cc-pvdz # * library 6-31G* * library 3-21G end task scf energy
Geometry Optimization
Running a geometry optimization just requires replacing the task directive. Here, we've also added a block of parameters controlling the minimization algorithm.
start opt_scf title "Pople SCF geometry optimization" geometry units angstrom load start.xyz end basis # * library cc-pvdz # * library 6-31G* * library 3-21G end driver loose maxiter 150 xyz opt end task scf optimize
DFT
You can also use DFT rather than HF (SCF) by changing the appropriate keywords and adding a DFT block to specify its functional:
start opt_dft
title "Pople DFT geometry optimization" geometry units angstrom load start.xyz end basis # * library cc-pvdz # * library 6-31G* * library 3-21G end dft xc xpbe96 1.0 \ pw91lda local 1.0 \ cpbe96 nonlocal 1.0 direct iterations 150 grid fine disp vdw 2 end driver loose maxiter 150 xyz opt end task dft optimize
The "xyz opt" causes NWChem to write out coordinate files, e.g. opt-001.xyz, ... as the optimization is proceeding.
Specifying Charge and Spin
Of course, we need to be able to specify the charge and total spin for most systems as well. Here's an input example appropriate for Fe3+ (5 spin-up electrons making up a half-filled d-shell):
start en_scf
title "Pople SCF energy"
geometry start units angstrom
load start.xyz
end
basis
# Fe library "Ahlrichs pVDZ" # better basis
* library 3-21G
end
set geometry start
charge 3
scf
sextet
end
task scf energy
Vibrational Frequencies
At a minimum, the second derivatives of the potential energy surface with respect to the nuclear coordinates make up a 3Nx3N matrix. The eigenvectors represent vibrational 'modes,' and the eigenvalues represent their force constants. Analyzing each mode as a harmonic oscillator leads to a set of vibrational frequencies, which give thermochemical information on the molecule as well as IR spectroscopic information.
From a minimized set of coordinates, all you should require is to add the appropriate task (and optionally a block of parameters)
task scf frequencies
