[Pw_forum] Re: About: the system is metallic, specify occupations?

Rahmat Gunawan s305igun at mail.chem.itb.ac.id
Wed Nov 22 14:09:40 CET 2006

Dear PW_Forum

Thanks to Guido... this is help me. now I try again input and it is work.

Thanks again

Success for your research

Sincerely Yours.

Rahmat Gunawan
PostGraduate Student
Dept. of Chemistry
Institut Teknologi Bandung
West Java, Indonesia

>>    H      0.000000000    0.000000000    3.250000000
>>    C      0.000000000    0.000000000    0.000000000
>>    C      0.333333333    0.666666666    0.000000000
>>    C      0.000000000    0.000000000    0.500000000
> You have an odd number N of electrons per unit cell, so your system IS
> metallic, and one cannot simply occupy the lowest N/2 bands as would be
> the default for an insulator.
> Hence you have to specify how to fill the electron bands.
> See file Doc/INPUT_PW, variables "occupation", "degauss", "smearing" and
> references given there for details.
> [If you want to think more about that, consider an H atom in a large box,
> suitable for an isolated-atom calculation. Then you have 1 electron per
> unit cell, which is odd again, so the system made of the repeated H
> atoms far away the one from the other is metallic, and you will find
> with PWscf that the lowest energy is given by half-filling a band which
> is nothing more than the (bonding) combination of the 1s orbitals, as it
> should be. Moreover, the results will not be much affected by the values
> you choose for the variables specified above. Can you imagine why?]
> Hope this helps,
> Guido
> Guido Fratesi
> Dipartimento di Fisica
> Universita` degli studi di Milano
> Via Celoria, 16 - 20133 MI (Italy)
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