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| 8:00:00 AM PDT - Tue, Jun 21st 2016 |
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Hi all
I am running DFT calculation using nwchem6.6 on CentOs including Fe atoms. I am experienced with the Turbomole program, but I am now in a position where I am using NWChem. I have been trying to run calculations with iron containing heme radical complexes, but I am running into convergence problems and spin-contamination. I am now doing some tests with iron-oxide radicals.
I have tried many combinations of RODFT, ROHF, SCF and DFT. I have tried to optimize with different charges, spin states and reusing vectors. I still have large spin contamination which I never experienced to this degree with Turbomole.
Expectation value of S2:
<S2> = 1.3408 (Exact = 0.7500)
I have found an input script for an iron molecule (fe2dft.nw) in the NWChem FAQ. I tried to run this and found that this script also produces spin contamination:
Expectation value of S2:
<S2> = 8.7503 (Exact = 8.7500)
Expectation value of S2:
<S2> = 8.7503 (Exact = 3.7500)
Expectation value of S2:
<S2> = 5.0004 (Exact = 0.0000)
I am wondering if it is an inherent problem with the NWChem code. I have not been able to find any publications that use NWchem to study heme complexes and I would like to know if anybody is running into similar problems.
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