[Pw_forum] metallic BP?

Sat Dec 3 09:39:37 CET 2011

         Hi Eric,                      sorry. I expressed my point maybe in a misleading way...I mean, i found a gap metallic (Homo is highest in energy than Lumo) but the system is reported to be a wide bandgap semiconductor (Gap > 2. eV)"highest occupied, lowest unoccupied level (ev):     6.1092    5.4104"HOMO=6.109  LUMO=5.4104  (as far as I understand)....the gap is 0.7 eV only if you switch HOMO and LUMO
The structure is the experimental one I found from a previous paper and it was optimized with Gaussian PBC

Thanks,G

----Messaggio originale----

Da: germaneau at gucas.ac.cn

Data: 03/12/2011 16.32

A: "giacsport at libero.it"<giacsport at libero.it>, "PWSCF Forum"<pw_forum at pwscf.org>

Ogg: Re: [Pw_forum] metallic BP?

    Hey Giacomo,

    Forgive my ignorance but why do you say that the "scf" calculation
    is a system that "should be" metallic
    ?

    To me it has a band gap of .7 ev.

    What do you mean by wide band gap semiconductor
    ? 

    What band gap value do you expect to get?

    May be the wide band gap behavior you mention does not occur at 0K.

    I guess you double checked whether your system is fully relaxed.

            Éric.

    On 12/02/2011 09:20 PM, giacsport at libero.it wrote:

      Dear All,
                 I am doing calculations on a 2 atom primitive cell of Boron 
Phosphide. What I obtain from the "scf" calculation is a system that "should 
be" metallic.... Indeed

     "highest occupied, lowest unoccupied level (ev):     6.1092    
5.4104"                 -->( As far as I understand, Homo lies 0.7 eV above the 
LUMO)

but of course this system is a wide-gap semiconductor.  
I am not able to figure out the reason for such behaviour. I have tested the 
same system (rhombohedral cell, a=b=c=6.06 Bohr, alpha=beta=gamma=60deg) in 
several machines finding always the same result. I attach the input file and 
the header of the two pseudos (USPP/GGA) I am using.
Thanks in advance for any comments.
My best,
Giacomo

&control
    calculation = 'scf'
    restart_mode='from_scratch',
    prefix='BP',
    tprnfor     = .true.,
    tstress     = .true.,
    wf_collect=.true.,
    pseudo_dir='/home/giacomo/GGA/',
    outdir='/home/giacomo/GGA/'
 /
&system
    ibrav=  4, celldm(1) =6.061296108, celldm(3)=1,
    nat=  2, ntyp= 2,
    ecutwfc =50.,  nbnd = 50,
 /
&electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
 /
ATOMIC_SPECIES
 B  10.811     B.UPF
 P  30.974     P.UPF
ATOMIC_POSITIONS (crystal)
 B  0.0  0.0  0.0
 P  0.25000  0.25000  0.250000
K_POINTS (automatic)
6 6 6 0 0 0

For BORON:

<PP_INFO>
Generated using Vanderbilt code, version   7  3  5
Author: unknown    Generation date:   20    6 2004
Automatically converted from original format
    0        The Pseudo was generated with a Non-Relativistic Calculation
  1.00000000000E+00    Local Potential cutoff radius
nl pn  l   occ               Rcut            Rcut US             E pseu
2S  2  0  2.00     10.00000000000      1.50000000000     -0.69693392995
2P  2  1  1.00     10.00000000000      1.53000000000     -0.26855658626
</PP_INFO>

<PP_HEADER>
   0                   Version Number
  B                    Element
   US                  Ultrasoft pseudopotential
    T                  Nonlinear Core Correction
 SLA  PW   GGX  GGC    PW91 Exchange-Correlation functional
    3.00000000000      Z valence
   -5.70038942945      Total energy
  0.0000000  0.0000000 Suggested cutoff for wfc and rho
    1                  Max angular momentum component
  781                  Number of points in mesh
    2    4             Number of Wavefunctions, Number of Projectors
 Wavefunctions         nl  l   occ
                       2S  0  2.00
                       2P  1  1.00
</PP_HEADER>
---------------------------------

For PHOSPHORUS

<PP_INFO>
Generated using Vanderbilt code, version   7  3  5
Author: unknown    Generation date:   20    6 2004
Automatically converted from original format
    1        The Pseudo was generated with a Scalar-Relativistic Calculation
  1.60000000000E+00    Local Potential cutoff radius
nl pn  l   occ               Rcut            Rcut US             E pseu
3S  3  0  2.00     10.00000000000      1.70000000000     -1.03015496458
3P  3  1  3.00     10.00000000000      1.70000000000     -0.40774343239
</PP_INFO>

<PP_HEADER>
   0                   Version Number
  P                    Element
   US                  Ultrasoft pseudopotential
    T                  Nonlinear Core Correction
 SLA  PW   GGX  GGC    PW91 Exchange-Correlation functional
    5.00000000000      Z valence
  -17.57767183737      Total energy
  0.0000000  0.0000000 Suggested cutoff for wfc and rho
    2                  Max angular momentum component
  903                  Number of points in mesh
    2    5             Number of Wavefunctions, Number of Projectors
 Wavefunctions         nl  l   occ
                       3S  0  2.00
                       3P  1  3.00
</PP_HEADER>

------------------------------------------
Giacomo Giorgi

Department of Chemical System Engineering,
School of Engineering, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

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          Dr.
            Éric Germaneau

          Graduate University of Chinese Academy of Sciences

          College of Physical Sciences

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