[CPMD-list] examples bands structure

[Thierry Deutsch]

Hello,

	I send you my answer for the same question.
I think this question should be in the FAQ.

Thierry Deutsch

----------  Message transmis  ----------

Subject: Re: [CPMD-list] Energy Bands
Date: Mercredi 24 Avril 2002 11:23
From: Thierry Deutsch <tdeutsch at cea.fr>
To: "abdenour sabir" <aksabir1 at hotmail.com>

Dear Abdenour,

     I send you an input file to calculate an accurate
density (first calculation):
 &CPMD
    OPTIMIZE WAVEFUNCTION
    FREE ENERGY FUNCTIONAL
    LANCZOS PARAMETER N=3
        10 8 0 1.e-10
        0.1   1.e-12
        0.01  1.e-14
        0.001 1.e-16
        0.005 1.e-18
        0.001 1.e-20
    CONVERGENCE
        1.e-4 1.e-3
    ELECTRON TEMPERATURE
        300
    DIIS MIXING
        10
    STORE WAVEFUNCTIONS OFF
    RHOOUT
    ENERGYBANDS
 &END
 &SYSTEM
   SYMMETRY
        BCC
   POINT GROUP
        AUTO
   SCALE
   TESR
        10
   ANGSTROM
   CELL
        3.30  1.0  1.0          0.0  0.0  0.0
   SPHERICAL CUTOFF
        63.
   KPOINTS MONKHORST-PACK
        64 64 64
   STATES
        9
 &END

 &ATOMS
*GOEDECKER/Nb_SG_Pade_q5 KLEINMAN-BYLANDER RAGGIO=1.2
   LMAX=D LOC=P
   1
   0.00D0       0.00D0          0.00D0
 &END



Then, I send you the input file to calculate the band
structure of Nb bcc.
 &CPMD
    OPTIMIZE WAVEFUNCTION
    FREE ENERGY FUNCTIONAL
    RESTART DENSITY
    LANCZOS DIAGONALIZATION
    LANCZOS PARAMETERS N=1 ALL
        50      8   0    1.D-18
    TROTTER FACTOR
        0.001
    BOGOLIUBOV CORRECTION
    CONVERGENCE
        5.D-5   5.D-4
    ELECTRON TEMPERATURE
        300.D0
    MAXSTEP
        1
    ENERGYBANDS
 &END
 &SYSTEM
   SYMMETRY
        BCC
   POINT GROUP
        AUTO
   SCALE
   TESR
        10
   ANGSTROM
   CELL
        3.30  1.0  1.0          0.0  0.0  0.0
   SPHERICAL CUTOFF
        63.
   density cutoff energy
        6820
   KPOINTS BANDS block=50
        51   0   0   0      0   0   1             Gamma to H
        51   0   0   1      0  .5  .5             H to N
        51   0  .5  .5     .5  .5  .5             N to P
        51  .5  .5  .5      0   0   0             P to Gamma
        51   0   0   0     .5  .5   0             Gamma to N
        51   0   0   1     .5  .5  .5             H to P
        0    0 0 0  0 0 0
   STATES
        9
 &END

 &ATOMS
*GOEDECKER/Nb_SG_Pade_q5  KLEINMAN-BYLANDER RAGGIO=1.2
   LMAX=D LOC=P
   1
   0.00D0       0.00D0          0.00D0
 &END


Now, You can replace the section &CPMD by :
&CPMD
    KOHN-SHAM ENERGIES
       6
    RESTART DENSITY
    ENERGYBANDS
&END

AND remove NSTATES in the section &SYSTEM.
You should obtain the same result.


In my case, I use the Trotter approximation, the result is
the same (except for the 10th decimal) as the Lanczos
diagonalisation of the Hamiltonian and the calculation is
faster.
You can remove FREE ENERGY CALCULATION, TROTTER FACTOR and
BOGOLIUBOV COORECTION if you want.

FOr the first calculation, I use also an electronic
temperature which improves the convergence. The result is
the same as 0 K (no chagnes in the band structure).
I have compare the Band structure of Nb bcc with FP-LMTO
calculation and we had a very good agreement. The
differences came from the pseudopotential approximation.

My last remark is about the memory. You need a lot of memories. To
decrease, you can add the option BLOCK=50 in the line
KPOINTS (I hope that this option works yet).
The RESTART file could be small if you use STORE
WAVEFUNCTIONS OFF which avoids to store all wavefunctions.

Good luck,
                Thierry Deutsch

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Thierry Deutsch
Laboratoire de simulation atomistique (L_Sim)
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