NWChem Tips

Various tips and file snippets for NWChem.

Efficient Jobs

I highly recommend the DIRECT keyword if you are running a DFT job. This tells NWChem to calculate integrals "on-the-fly" and store in memory, rather than trying to calculate and store these integrals in data files. Writing large files to disk is time intensive, which slows down jobs. Fast, modern machine should be able to quickly calculate these integrals and store them in memory.

COSMO Solvation

Try this.

cosmo
 dielec 2.27
end

This will use the default cavity radii. You can change these with the following commands.

cosmo
 dielec 78.0
 radius 1.40
       1.16
       1.16
end

Thermodynamic Values

Sometimes you need enthalpy and free energy. See for instance here: http://verahill.blogspot.com/2012/09/example-attempt-of-isodesmic-reactions.html.

Add the following lines.

 task dft energy
 task dft freq

You'll get something like the following in your output.

Total DFT energy =     -229.081786570898

Temperature                      =   298.15K
frequency scaling parameter      =   1.0000

Zero-Point correction to Energy  =   38.922 kcal/mol  (  0.062026 au)
Thermal correction to Energy     =   41.772 kcal/mol  (  0.066567 au)
Thermal correction to Enthalpy   =   42.364 kcal/mol  (  0.067511 au)
 
Total Entropy                    =   68.603 cal/mol-K
  - Translational                =   38.179 cal/mol-K (mol. weight =  60.0211)
  - Rotational                   =   23.852 cal/mol-K (symmetry #  =        1)
  - Vibrational                  =    6.572 cal/mol-K

Cv (constant volume heat capacity) =   14.200 cal/mol-K
  - Translational                  =    2.979 cal/mol-K
  - Rotational                     =    2.979 cal/mol-K
  - Vibrational                    =    8.241 cal/mol-K

This will give you the following values (all hartree).

E = -229.0817866

H = -229.0817866+0.067511

G = -229.0817866+0.067511-T*(68.603/(1000*627.509469))

Sample Organometallic Input

echo
title "Cisplatin-c2v"
#PERMANENT_DIR /dtemp/d3p271/nwchem/t13/tmp8
#memory total 4000 MB

basis "ao basis" print
  Pt library lanl2dz_ecp file /home/nadeskins/work1/nwchem/libraries/
  N library "6-31G*" file /home/nadeskins/work1/nwchem/libraries/
  H library "6-31G*" file /home/nadeskins/work1/nwchem/libraries/
  Cl library "6-31G*" file /home/nadeskins/work1/nwchem/libraries/
end

ecp
  Pt library lanl2dz_ecp file /home/nadeskins/work1/nwchem/libraries/
end

geometry noautoz
 Pt        -1.21199       -0.68451        0.00000
 Cl        -2.78250        1.17327       0.00
 Cl         0.84906        0.57816       0.0
 N         -2.64382       -2.27924       0.0
 H         -2.17425       -3.15758       -0.02818
 H         -3.15231       -2.12622        0.84020
 H         -3.49754       -2.45482       -0.75581
 N         -0.07733       -2.52728        0.0
 H          0.94267       -2.52728        0.02513
 H         -0.41733       -3.32743        0.55857
 H         -0.41733       -2.58918       -0.93454
 symmetry c2v
end
 
DRIVER
 XYZ cisplatin-c2v
 MAXITER 100
END

dft
 xc b3lyp
 DIRECT
 CONVERGENCE gradient 1e-6
 ITERATIONS 1000
end

task dft optimize