[Pw_forum] phonon at G error : from phq_readin : error # 1 no elec. field with metals

[Nicola Marzari]

xu yuehua wrote:
> yes,before pho calculation ,i have computed "scf" .the water. in is this
>  &system
> ibrav     = 0,
>   nat       = 15,
>   ntyp      = 2,
>   ecutwfc   = 29.98744D0,
>   ecutrho   =200
>   occupations = "smearing",
>   smearing    = "gauss",
>   degauss     = 0.003D0,
> if it is unsuitable ,i have no idea to use what occupations and so on 
> .please help me .thanks



> my name is xu yuehua
> affilation: physics depatment
>  nanjing university china.

Dear Xu,

welcome to the gang.

There are two comments to make here - if you want your calculation to 
work, start by droppping the keywords for occupations, smearing, and
degauss. Those three are used for systems with fractional occupations -
these are typically metals, and that's why phonon stopped. By the
way, "Phonon" calculation for the water molecule and the water dimer
are available in a 2005 JCP by Sit and Marzari - you could compare your
results and parameters with those.

The second comment is that even completing your calculations 
successfully won't be very helpful, if you do not first become
experienced in this kind of calculations.

Now, I'm not sure what to suggest - there is a book on "Electronic
Structure" by Richard Martin that is outstanding, but a bit advanced.
A more introductory one has recently come out, by Jorge Kohanoff
("Electronic Structure Calculations for Solids and Molecules).

I might sound self-serving, but our graduate class on atomistic
modeling of materials (including video lectures, and pwscf homework),
is fully on the web, linked from
http://quasiamore.mit.edu/pmwiki/index.php?n=Main.Teaching ).
This class takes MIT students of different backgrounds, and that
have never seen computational modeling, through a basic knowledge
of the fundamentals.

				nicola


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Prof Nicola Marzari   Department of Materials Science and Engineering
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tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu