[Pw_forum] Help to learn

[lan haiping]

Hi, Happy new year ~!


On Jan 6, 2008 10:10 AM, Faridul Isalm <faridul at email.com> wrote:

> Dear Sir,
> I am a novice user of Quantum Espersso (PWscf).I use it on the CYGWIN
> platform. I did the examples successfully those are given with Quantum
> Espresso package. I am now trying to learn "band structure calculation"
> step. But I face the following problems:
>
> 1) when I run plotband.x, there need to specify "Efermi", but where I get
> this value. I look all output files, nowhere that is. such as for Si Efermi
> = 6.337, from where this value comes.
>
 you can find fermi level at output, if not, i think it is due to your
smearing scheme of the calculation. For semiconductor, the fermi level
should be at the middle of bandgap.  For metal
system, i think  pwscf should always be able to give you the value of fermi
level in you output file.


>
> 2)when this method is used for other materials such as SiO2, MnO2, GaAs,
> etc., then how can i specify their ibrav in the &system namelist. and also
> how can I know their celldm.

 i think you should read the last part of INPUT_PW.. it gives you detail
description of  crystal
system building.  of coz, you should know the coordinates of these systems
before you starting to handle .. you may obtain  coordinates from this
http://cst-www.nrl.navy.mil/lattice/  .


>
>
> 3)when it is used for semiconductor materials, then which variables may
> need to specify in the &system namelist.
>
   there are several  examples for semiconductors in $QE/examples, i think
you can benefit from these tests.


>
> 4)how can I determine the proper "ecutwfc" of a particular material. is it
> =kT?


hmmm,   ecutwfc is one of the most key parameters  in periodic boundary
calculation,
 which determines your calculation's accuracy.    it should not be equal to
kT, i think it is too
small to believe.   why not to read again  INPUT_PW ?


>
> 5)I face a great problem when I use k-points {automatic}, then output of
> the band does not match with the given examples. But when I use 36 k-points
> that are given in the examples then it is ok. Now how can I choose the
> proper k-points for a particular material.
>

 for this problem, i think you should figure out 2 different calculations ,
scf and nscf, for  scf calculation , we use kpoint to sample  BZ to obtain
convergent electron density , for nscf calculation , we use k-point path to
obtain bandstructure and other quantities . k-point path
is the reciprocal path between high symmetry points of your sytem.


>
> 6)When I run xcrysden --pwo si.scf.out, then i get " the hardware does not
> support the stereo" error massage. My computer is "Intel Core2 Duo,
> 1.86GHz, 512MB RAM". how can i solve this problem.
>
while, this problem should be due to your video card, or your improper
installing related driver
program of video card



>
> I will be very greatful to you, if you kindly give me the solutions of the
> above mentioned problems. I want to learn about this method clearly. I will
> be very happy if you give me yours further valuable   successions that can
> help me to learn.





>
>
> I am looking forward to hearing from you.
> Thank you for your valuable time.
>
> Sincerely
> Dr. A.K.Md Farid ul Islam
> Assistant Professor,
> Dept. of Physics,
> Carmichael University College, Rangpur-5004, Bangladesh
>
>
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bests,  hai-ping

-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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