Dear PWSCF users,<div> 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 <b>vc-relax</b> and input, output for <b>'scf'</b> calculation are <b>respectively</b><br>
<br><b>INPUT FOR VC-RELAX</b><br><br>&control<br> calculation = 'vc-relax',<br> restart_mode='restart',<br> nstep=200<br> outdir='/home/rajpala/Desktop/gan_wur',<br> pseudo_dir='/home/rajpala/Desktop/gan_wur'<br>
prefix='gan',<br> tstress = .true.,<br> tprnfor = .true.,<br> /<br> &system <br> ibrav= 4, a = 3.3, c = 5.3,nat= 4, ntyp= 2,<br> ecutwfc = 30,ecutrho=240,occupations='smearing',degauss=0.01,smearing='gaussian' <br>
/<br> &electrons<br> diagonalization='david'<br> mixing_mode = 'plain'<br> mixing_beta = 0.7<br> conv_thr = 1.0d-7<br> /<br>&IONS<br> ion_dynamics='bfgs'<br> trust_radius_min=1.D-7<br>
/<br> &CELL<br> cell_dynamics='bfgs'<br> /<br>ATOMIC_SPECIES<br> Ga 69.723 Ga.pbe-nsp-van.UPF<br> N 14.0067 N.pbe-rrkjus.UPF<br> ATOMIC_POSITIONS (crystal)<br> Ga 0.00 0.00 0.00 <br> Ga 1/3 2/3 1/2 <br> N 0.0 0.0 69/200 <br>
N 1/3 2/3 169/200 <br> K_POINTS (automatic)<br> 6 6 4 0 0 0<br><br><b>SEGMENT OF OUTPUT</b> <b>OF VC-RELAX</b><br><br>! total energy = -395.68385837 Ry<br> Harris-Foulkes estimate = -395.68385837 Ry<br>
estimated scf accuracy < 6.2E-10 Ry<br><br> The total energy is the sum of the following terms:<br><br> one-electron contribution = -190.48989791 Ry<br> hartree contribution = 134.51657806 Ry<br>
xc contribution = -108.33929602 Ry<br> ewald contribution = -231.37124250 Ry<br> smearing contrib. (-TS) = -0.00000000 Ry<br><br> convergence has been achieved in 3 iterations<br>
<br> Forces acting on atoms (Ry/au):<br><br> atom 1 type 1 force = -0.00000000 0.00000000 0.00003463<br> atom 2 type 1 force = 0.00000000 -0.00000000 -0.00003656<br> atom 3 type 2 force = -0.00000000 -0.00000000 0.00000483<br>
atom 4 type 2 force = 0.00000000 0.00000000 -0.00000291<br><br> Total force = 0.000051 Total SCF correction = 0.000052<br> SCF correction compared to forces is too large, reduce conv_thr<br>
<br><br> entering subroutine stress ...<br><br> total stress (Ry/bohr**3) (kbar) P= -0.20<br> -0.00000138 -0.00000000 -0.00000000 -0.20 -0.00 -0.00<br> -0.00000000 -0.00000138 -0.00000000 -0.00 -0.20 -0.00<br>
-0.00000000 -0.00000000 -0.00000124 -0.00 -0.00 -0.18<br><br><br> bfgs converged in 24 scf cycles and 13 bfgs steps<br> (criteria: energy < 0.10E-03, force < 0.10E-02, cell < 0.50E+00)<br>
<br> End of BFGS Geometry Optimization<br><br> Final enthalpy = -395.6838583715 Ry<br> new unit-cell volume = 315.86297 a.u.^3 ( 46.80606 Ang^3 )<br><br>CELL_PARAMETERS (alat)<br> 0.973879690 0.000000000 0.000000000<br>
-0.486939845 0.843404552 -0.000000000<br> -0.000000000 -0.000000000 1.585692727<br><br>ATOMIC_POSITIONS (crystal)<br>Ga -0.000000000 -0.000000000 -0.015912479<br>Ga 0.333333333 0.666666667 0.484088029<br>
N 0.000000000 0.000000000 0.360941274<br>N 0.333333333 0.666666667 0.860883176<br><br> <b>INPUT FOR SCF<br><br></b>&control<br> calculation = 'scf',<br> restart_mode='restart',<br>
outdir='/home/rajpala/Desktop/gan',<br> pseudo_dir='/home/rajpala/Desktop/gan'<br> prefix='gan',<br> tstress = .true.,<br> tprnfor = .true.,<br> /<br> &system <br> ibrav= 4, a = 3.213802977, c = 5.232785999,nat= 4, ntyp= 2,<br>
ecutwfc = 30,ecutrho=240,occupations='smearing',degauss=0.01,smearing='gaussian' <br> /<br> &electrons<br> diagonalization='david'<br> mixing_mode = 'plain'<br> mixing_beta = 0.7<br>
conv_thr = 1.0d-7<br> /<br>ATOMIC_SPECIES<br> Ga 69.723 Ga.pbe-nsp-van.UPF<br> N 14.0067 N.pbe-rrkjus.UPF<br> ATOMIC_POSITIONS (crystal)<br>Ga -0.000000000 -0.000000000 -0.015912479<br>Ga 0.333333333 0.666666667 0.484088029<br>
N 0.000000000 0.000000000 0.360941274<br>N 0.333333333 0.666666667 0.860883176<br> K_POINTS (automatic)<br> 6 6 4 0 0 0<b><br></b><br><b>OUTPUT FOR SCF</b><br><br>! total energy = -395.68329166 Ry<br>
Harris-Foulkes estimate = -395.68329169 Ry<br> estimated scf accuracy < 0.00000005 Ry<br><br> The total energy is the sum of the following terms:<br><br> one-electron contribution = -190.48963216 Ry<br>
hartree contribution = 134.51703338 Ry<br> xc contribution = -108.33945035 Ry<br> ewald contribution = -231.37124253 Ry<br> smearing contrib. (-TS) = -0.00000000 Ry<br>
<br> convergence has been achieved in 8 iterations<br><br> Forces acting on atoms (Ry/au):<br><br> atom 1 type 1 force = 0.00000000 0.00000000 -0.00006952<br> atom 2 type 1 force = 0.00000000 0.00000000 -0.00008099<br>
atom 3 type 2 force = 0.00000000 0.00000000 -0.00003004<br> atom 4 type 2 force = 0.00000000 0.00000000 0.00018054<br><br> Total force = 0.000212 Total SCF correction = 0.000060<br>
<br><br> entering subroutine stress ...<br><br> total stress (Ry/bohr**3) (kbar) P= -1.64<br> -0.00001229 0.00000000 0.00000000 -1.81 0.00 0.00<br> 0.00000000 -0.00001229 0.00000000 0.00 -1.81 0.00<br>
0.00000000 0.00000000 -0.00000878 0.00 0.00 -1.29<br><br><b>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.<br>
Can anybody please tell me where I am going wrong.</b><br><br>Thanks in advance,<br>Sincerely,<br>mohnish<br><br clear="all">
<br>-- <br>Mohnish Pandey<br>Y6927262,4th Year dual degree student,<br>Department of Chemical Engineering,<br>IIT KANPUR<br>09235721300<br>
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