[Pw_forum] Suitable pseudopotentials for LiH..H2O

Mon Jun 20 13:56:28 CEST 2011

Dear Savita
It is generally suggested that high-level post-HF methods (as MP2)  
account for van der Waals interactions far better than standard DFT  
calculations (i.e., LDA or GGA calculations). Within QE (actually, by  
using pw.x), you could try to use either a semi-empirical dispersion  
correction (london=.true. flag), or an improved xc functional  
containing a long-range correlation contribution (input_dft="vdw-df"  
flag) in order to simulate van der Waals interactions in a reliable way.
HTH
Giuseppe

Giuseppe Mattioli
ISM-CNR
Italy

Quoting psavita at crlindia.com:

> Dear Prof. Ghosh,
>
> I should have done this before, but now I have performed structure
> relaxation of LiH..H2O using DFT with 6-31++g basis set,
> the same one that was used for mp2 calculations, and found that DFT
> does not give intramolecular H-bond.
> Thus, in general, DFT does not seem suitable for such systems and
> hence there has been difficulty with QE.
>
> I agree with Paolo that the problem is not with plane wave approach.
>
> Thanks once again 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: -----
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> Date: 06/20/2011 01:17PM
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> Today's Topics:
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>    1. Re: Suitable pseudopotentials for LiH..H2O (Prasenjit Ghosh)
>    2. Re: Testing pseudopotential (Julen Ibanez Azpiroz)
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 20 Jun 2011 11:59:51 +0530
> From: Prasenjit Ghosh <prasenjit.jnc at gmail.com>
> Subject: Re: [Pw_forum] Suitable pseudopotentials for LiH..H2O
> To: PWSCF Forum <pw_forum at pwscf.org>
> Message-ID: <BANLkTin0W8OO=H88_J38cxXnmWsMYT12rg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> 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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>> >
>> >
>>
>>
>> --
>> 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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> Message: 2
> Date: Mon, 20 Jun 2011 09:21:23 +0200
> From: Julen Ibanez Azpiroz <jibanez008 at ikasle.ehu.es>
> Subject: Re: [Pw_forum] Testing pseudopotential
> To: PWSCF Forum <pw_forum at pwscf.org>
> Message-ID: <BANLkTimVxsG6gV0cXGeyV=0_HQ8UdrpmGw at mail.gmail.com>
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>
> Hi Padmaja,
>
> I think that in general it cannot be said that a PP is good or bad
> looking
> just at the value you mention of AE-PS. Maybe you can try testing
> your PP in
> some system in which you know the answer, for instance calculate the
> band
> structure of bulk Cr and compare with known results. I see that in
> the
> repository of QE PP there are a couple of scalar-relativistic Cr
> PP's, you
> can check if their band structures match with yours (with
> lspinorb=.false.
> in the case of your fully relat PP). Also you can try to compare this
> band
> structure with some all-electron band structure. And finally, it is
> very
> good to compare the lattice parameter obtained with your PP in bulk
> Cr with
> the real value, I think they should differ at most in 5%. Hope this
> helps,
>
> --
>
> ?========================================
>  Julen Iba?ez Azpiroz
>  Materia Kondentsatuaren Fisika Saila
>  Zientzia eta Teknologia Fakultatea
>  Euskal Herriko Unibertsitatea
>  644 Posta Kutxatila, 48080 Bilbo, Spain
>
>  Telefonoa: +34 946015326
>  Mail: jibanez008 at ikasle.ehu.es
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