[Pw_forum] Suitable pseudopotentials for LiH..H2O

[Prasenjit Ghosh]

Dear Savita,

It is hard to tell....You can try plotting total energy vs. the box size and
see how the energies are changing....if the change is of the order of a meV
then I would say that your calculations are converged wrt box size.......

However, I think it is good idea to follow Stefano's suggestion........using
the same basis set you have been using for your mp2 calculation, you try to
calculate the same thing using DFT and see whether you get similar
results.....if you get different results, then it will suggest that DFT is
not properly describing the electronic correlations.

Prasenjit

On 20 June 2011 10:24, <psavita at crlindia.com> wrote:

> Dear Prof. Ghosh,
>
> As per your suggestion, I performed the structure relaxation of LiH--H2O
> system using a bigger cubic box of dimension 50 a.u.
> and I still find H2 abstraction instead of an intramolecular dihydrogen
> bond.
> Do you think the box is still inadequate?
> For such systems, would it be better to put some constraints initially?
> How do we do this in QE?
>
> Thanks for your suggestion and best regards,
>
> Savita Pundlik
> Computational Materials Applied Research Group
> Computational Research Laboratories Ltd.,
> Taco House, Damle Path, Off Law College Road
> Pune - 411004, India.
>
>
>
> -----pw_forum-bounces at pwscf.org wrote: -----
>
>
>
>
>
>
> Dear Savita,
>
> I am not an expert on these type of systems.......however just a small
> piece
> of advice.....a single molecule of water has a huge dipole moment.....so a
> box size of 25 bohr may not be sufficient, until and unless binding to LiH
> quenches the dipole moment......so you may like to check whether your box
> is
> sufficiently big.....usually for a single molecule of water one uses about
> 35-40 bohr box or can use dipole correction.
>
> Prasenjit
>
> On 17 June 2011 11:42, <psavita at crlindia.com> <psavita at crlindia.com>wrote:
>
> > Hello,
> >
> > I have been trying to get the optimum structure of LiH..H2O that has an
> > intramolecular dihydrogen bond, using pwscf.
> > I could get the proper structure earlier using mp2 theory and 6-31++g
> > basis.
> >
> > For pwscf, the species is enclosed in a cubic box of 25 bohr for gamma
> > point calculation.
> > I tried the pz lda, pbe gga as well we blyp PS for the atoms in this
> > system, however, the first and the last
> > lead to H2O..LiH, the latter LiH being linear while pbe gives LiH + H2,
> but
> > no dihydrogen bond. Is there any other PS
>
> > that may lead to proper structure? Or is it that plane wave approach does
> > not suit systems of this kind?
> >
> > Thanks in advance and best regards,
> >
> > Savita Pundlik
> > Computational Materials Applied Research Group
> > Computational Research Laboratories Ltd.,
> > Taco House, Damle Path, Off Law College Road
> > Pune - 411004, India.
> >
> >
> >
> > _______________________________________________
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> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
> >
>
>
> --
> PRASENJIT GHOSH,
> Assistant Professor,
> IISER Pune,
> First floor, Central Tower, Sai Trinity Building
> Garware Circle, Sutarwadi, Pashan
> Pune, Maharashtra 411021, India
>
> Phone: +91 (20) 2590 8203
> Fax: +91 (20) 2589 9790
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-- 
PRASENJIT GHOSH,
Assistant Professor,
IISER Pune,
First floor, Central Tower, Sai Trinity Building
Garware Circle, Sutarwadi, Pashan
Pune, Maharashtra 411021, India

Phone: +91 (20) 2590 8203
Fax: +91 (20) 2589 9790
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