[Pw_forum] negative phonon frequency in GaN bulk
mohnish pandey
mohnish.iitk at gmail.com
Sat Apr 10 15:47:05 CEST 2010
Dear PWSCF users,
I am trying to get phonon dispersion
relation of Gallium Nitride. First I have done the vc-relax calculation for
GaN to get equilibrium lattice parameter. Then using that equilibrium
lattice parameter I have done 'scf' calculation after which I have to do
phonon calculation, but the problem is after doing the 'scf' calculation
there is some pressure (greater than the threshold pressure for vc-relax)
calculation. My input, output f for *vc-relax* and input, output for
*'scf'*calculation are
*respectively*
*INPUT FOR VC-RELAX*
&control
calculation = 'vc-relax',
restart_mode='restart',
nstep=200
outdir='/home/rajpala/Desktop/gan_wur',
pseudo_dir='/home/rajpala/Desktop/gan_wur'
prefix='gan',
tstress = .true.,
tprnfor = .true.,
/
&system
ibrav= 4, a = 3.3, c = 5.3,nat= 4, ntyp= 2,
ecutwfc =
30,ecutrho=240,occupations='smearing',degauss=0.01,smearing='gaussian'
/
&electrons
diagonalization='david'
mixing_mode = 'plain'
mixing_beta = 0.7
conv_thr = 1.0d-7
/
&IONS
ion_dynamics='bfgs'
trust_radius_min=1.D-7
/
&CELL
cell_dynamics='bfgs'
/
ATOMIC_SPECIES
Ga 69.723 Ga.pbe-nsp-van.UPF
N 14.0067 N.pbe-rrkjus.UPF
ATOMIC_POSITIONS (crystal)
Ga 0.00 0.00 0.00
Ga 1/3 2/3 1/2
N 0.0 0.0 69/200
N 1/3 2/3 169/200
K_POINTS (automatic)
6 6 4 0 0 0
*SEGMENT OF OUTPUT* *OF VC-RELAX*
! total energy = -395.68385837 Ry
Harris-Foulkes estimate = -395.68385837 Ry
estimated scf accuracy < 6.2E-10 Ry
The total energy is the sum of the following terms:
one-electron contribution = -190.48989791 Ry
hartree contribution = 134.51657806 Ry
xc contribution = -108.33929602 Ry
ewald contribution = -231.37124250 Ry
smearing contrib. (-TS) = -0.00000000 Ry
convergence has been achieved in 3 iterations
Forces acting on atoms (Ry/au):
atom 1 type 1 force = -0.00000000 0.00000000 0.00003463
atom 2 type 1 force = 0.00000000 -0.00000000 -0.00003656
atom 3 type 2 force = -0.00000000 -0.00000000 0.00000483
atom 4 type 2 force = 0.00000000 0.00000000 -0.00000291
Total force = 0.000051 Total SCF correction = 0.000052
SCF correction compared to forces is too large, reduce conv_thr
entering subroutine stress ...
total stress (Ry/bohr**3) (kbar) P=
-0.20
-0.00000138 -0.00000000 -0.00000000 -0.20 -0.00 -0.00
-0.00000000 -0.00000138 -0.00000000 -0.00 -0.20 -0.00
-0.00000000 -0.00000000 -0.00000124 -0.00 -0.00 -0.18
bfgs converged in 24 scf cycles and 13 bfgs steps
(criteria: energy < 0.10E-03, force < 0.10E-02, cell < 0.50E+00)
End of BFGS Geometry Optimization
Final enthalpy = -395.6838583715 Ry
new unit-cell volume = 315.86297 a.u.^3 ( 46.80606 Ang^3 )
CELL_PARAMETERS (alat)
0.973879690 0.000000000 0.000000000
-0.486939845 0.843404552 -0.000000000
-0.000000000 -0.000000000 1.585692727
ATOMIC_POSITIONS (crystal)
Ga -0.000000000 -0.000000000 -0.015912479
Ga 0.333333333 0.666666667 0.484088029
N 0.000000000 0.000000000 0.360941274
N 0.333333333 0.666666667 0.860883176
*INPUT FOR SCF
*&control
calculation = 'scf',
restart_mode='restart',
outdir='/home/rajpala/Desktop/gan',
pseudo_dir='/home/rajpala/Desktop/gan'
prefix='gan',
tstress = .true.,
tprnfor = .true.,
/
&system
ibrav= 4, a = 3.213802977, c = 5.232785999,nat= 4, ntyp= 2,
ecutwfc =
30,ecutrho=240,occupations='smearing',degauss=0.01,smearing='gaussian'
/
&electrons
diagonalization='david'
mixing_mode = 'plain'
mixing_beta = 0.7
conv_thr = 1.0d-7
/
ATOMIC_SPECIES
Ga 69.723 Ga.pbe-nsp-van.UPF
N 14.0067 N.pbe-rrkjus.UPF
ATOMIC_POSITIONS (crystal)
Ga -0.000000000 -0.000000000 -0.015912479
Ga 0.333333333 0.666666667 0.484088029
N 0.000000000 0.000000000 0.360941274
N 0.333333333 0.666666667 0.860883176
K_POINTS (automatic)
6 6 4 0 0 0*
*
*OUTPUT FOR SCF*
! total energy = -395.68329166 Ry
Harris-Foulkes estimate = -395.68329169 Ry
estimated scf accuracy < 0.00000005 Ry
The total energy is the sum of the following terms:
one-electron contribution = -190.48963216 Ry
hartree contribution = 134.51703338 Ry
xc contribution = -108.33945035 Ry
ewald contribution = -231.37124253 Ry
smearing contrib. (-TS) = -0.00000000 Ry
convergence has been achieved in 8 iterations
Forces acting on atoms (Ry/au):
atom 1 type 1 force = 0.00000000 0.00000000 -0.00006952
atom 2 type 1 force = 0.00000000 0.00000000 -0.00008099
atom 3 type 2 force = 0.00000000 0.00000000 -0.00003004
atom 4 type 2 force = 0.00000000 0.00000000 0.00018054
Total force = 0.000212 Total SCF correction = 0.000060
entering subroutine stress ...
total stress (Ry/bohr**3) (kbar) P=
-1.64
-0.00001229 0.00000000 0.00000000 -1.81 0.00 0.00
0.00000000 -0.00001229 0.00000000 0.00 -1.81 0.00
0.00000000 0.00000000 -0.00000878 0.00 0.00 -1.29
*As you can see there is perssure is different in final vc-relax and scf
calculation. After that I am doing phonon calculation and I am getting some
frequencies to be negative.
Can anybody please tell me where I am going wrong.*
Thanks in advance,
Sincerely,
mohnish
--
Mohnish Pandey
Y6927262,4th Year dual degree student,
Department of Chemical Engineering,
IIT KANPUR
09235721300
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20100410/b907bf02/attachment.html>
More information about the users
mailing list