[Pw_forum] Question on phonon calculation of MgB2.

[张 洪彬]

Dear all:
  Now I am doing some calculation on the phonon dispersion curves of 
MgB2.To get a more detailed and correct picture, I have tried several 
different values of ecutwfc ecutrho and degauss, however there are some 
problems I want an answer:
  let me show the results first: (ecutrho=300 for the parameters below)
* ecutwfc  ***** degauss *** E1u ******* A2u  ****** E2g  ********  B1g  
**************
   60             0.005      309         383         585             693
   60             0.01       309         383         551             692
   60             0.02       309         383         541             692

   70             0.005     *******as above****      566            as 
above
   70             0.01        *           *          532              *
   70             0.02        *           *          522              *
  
   80             0.005       *           *          570              *
   80             0.01        *           *          536              *
   80             0.02        *           *          527              *
*****************************************************************************************

   so it seems like that E1u, A2u, and B1g have reached the convergence, 
while E2g varies as degauss value, since electron-phonon coupling for this 
modes is very strong, so is this the reason why it varies? and which value 
should I choose? Or is it related to the values of structure vectors? Or 
pseudopotentials?
    Further more, for ecutwfc=50, I didn't get the converged value for A2u 
mode(692), but I think ecutwfc=50 is so large a value, is there anything 
else to improve? PP?
    my input file as follows:
**omitted some here**
 ecutws="60\
          70\
          80"
 gausss="0.005\
         0.01\
         0.02"
for ecutw in $ecutws;do
for gauss in $gausss;do
 
# clean TMP_DIR
$ECHO "  cleaning $TMP_DIR...\c"
rm -rf $TMP_DIR/*
$ECHO " done"

# self-consistent calculation
cat > mgb.scf.in << EOF
 &control
    calculation='scf'
    restart_mode='from_scratch',
    tstress = .true.
    tprnfor = .true.
    prefix='mgb',
    pseudo_dir = '$PSEUDO_DIR/',
    outdir='$TMP_DIR/'
 /
&SYSTEM
                       ibrav = 4,
                   celldm(1) = 5.803350584,
                   celldm(3) = 1.165092804,
                         nat = 3,
                        ntyp = 2,
                     ecutwfc = $ecutw ,
                     ecutrho = 300,
                 occupations = 'smearing' ,
                     degauss = $gauss ,
                    smearing = 'gaussian' ,
 /
 &ELECTRONS
                    conv_thr = 1.0d-8 ,
                 mixing_beta = 0.7 ,
             diagonalization = 'cg' ,
 /
ATOMIC_SPECIES
   Mg   24.30500  Mg.pz-bhs.UPF 
    B   10.81100  B.pz-bhs.UPF 
ATOMIC_POSITIONS alat 
   Mg      0.000000000    0.000000000    0.000000000    
    B      0.500000000    0.288680000    0.570500000    
    B      0.000000000    0.577350000    0.570500000    
K_POINTS automatic 
  30 30 30 0 0 0 
EOF
$ECHO "  running the scf calculation...\c"
$PW_COMMAND < mgb.scf.in > mgb.scf.out
$ECHO " done"

# phonons
cat > mgb.phG.in << EOF
phonons of mgb at Gamma
 &inputph
  tr2_ph=1.0d-12,
  prefix='mgb',
  amass(1)=24.305,
  amass(2)=10.811,
  outdir='$TMP_DIR/',
  fildyn='mgb.$ecutw.$ecutr.$gauss.dynG',
 /
0.0 0.0 0.0
EOF
$ECHO "  running the phonon calculation at Gamma...\c"
$PH_COMMAND < mgb.phG.in > mgb.phG.out
$ECHO " done"

#using dynmat.x to recalculate phonon at /gamma
$ECHO "  running dynmat.x calculation at Gamma...\c"
cat > mgb.$ecutw.$ecutr.$gauss.dynmat.in << EOF
&input  
  fildyn='mgb.$ecutw.$ecutr.$gauss.dynG' 
  asr=.true.
  amass(1)=24.305
  amass(2)=10.811
  filout='mgb.$ecutw.$ecutr.$gauss.dynmat'
  filmol='mgb.$ecutw.$ecutr.$gauss.modes'
/
EOF
$DYNMAT_COMMAND < mgb.$ecutw.$ecutr.$gauss.dynmat.in 
>mgb.$ecutw.$ecutr.$gauss.dynmat.out
$ECHO "done for $ecutw $ecutr.$gauss"
done
done

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