PSPW QM/MM Lennard-Jones Ion Parameters
Just Got Here
11:00:58 AM PDT - Tue, Aug 27th 2013
Hi,

I'm a new NWchem user trying to run a decently large QM/MM simulation. My QM region consists of ~150 atoms, and my MM region will be ~500 ethanol molecules. I'd like to apply this procedure to larger systems in the future, so I figured I would use the QM/MM capabilities in the PSPW module. The documentation has a very instructive example (http://nwchemgit.github.io/images/Ccl4-64water.nw), however I'm a bit confused about how to translate this procedure to my molecule.

More specifically, I've no idea where the Lennard-Jones ion parameters came from, and thus I've no clue where to obtain the relevant values for my molecule. Additionally, it's unclear to me if two carbon atoms in different chemical environments would have different LJ parameters, or if the LJ parameters of atoms in the QM region change as a function of solvent molecules in the MM region.

I'm aware of the more standard QM/MM Gaussian-based module and am working to get that going for my systems, too, but any help with the PSPW module and these ion parameters would be greatly appreciated.

Thanks!

Sam

Just Got Here
10:32:24 PM PDT - Mon, Sep 2nd 2013
Answering my own question - LJ parameters can be found throughout the literature, especially from papers about the OPSL-AA forcefield. If anyone else is struggling to find them, feel free to respond and I can send over some helpful papers.

Clicked A Few Times
5:41:50 AM PST - Sun, Mar 2nd 2014
Dear All

We are a small group starting to play MD with nwchem. Unfortunately we are new with MD. Hereby I would like to have the form of Lennard-Jones equation from which parameter files are written in nwchem. Also, symbols for definition of TiO2 bulck and surface atoms in .par and .frg files. Also, the form of definition of an organic liquid which is adsorbed on the TiO2: number of organic molecules in the PDB and FRG files. I am searching for several weeks in nwchem forum and other places, but I can not find any help except to the QMMM appendix page which is not useful for me. 






Best Regards

Just Got Here
7:17:42 AM PDT - Thu, Sep 22nd 2016
Dear Sam:
   Have you solved this problem? I also encountered the same problem. Two carbon atoms in different chemical environments in QM region would have different LJ parameters. Can you tell me how to do? Can you tell me your email address? My email address is lujb15@163.com

   Thank you!


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