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flying_lw

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专业: 理论和计算化学

[求助] MgB2超导转变温度

最近在学习用quantum espresso计算超导转变温度，所以就用比较成熟的MgB2体系作为例子进行实际的计算。但是计算结果与实验值差距很大，实验值是39.3 K，而我最高只能算到4.1 K，想尽各种办法也没能有效提高，不知道是参数设置的不对还是赝势选择有问题。看到有些文献用QE计算的MgB2的转变温度与实验值复合的很好。但是自己计算的就是不对，有这方面经验的虫友请帮忙看一下输入文件，有什么地方是可以改进或是改正的。谢谢了！

cat > mgb2.scf.fit.in << EOF
&control
calculation='scf'
restart_mode='from_scratch',
prefix='mgb2',
etot_conv_thr = 1.0d-8
forc_conv_thr = 1.0d-7
pseudo_dir = '$PSEUDO_DIR/',
outdir='$TMP_DIR/'
/
&system
ibrav=  4, celldm(1) =5.8124, celldm(3)=1.1483, nat= 3, ntyp= 2,
ecutwfc =60.0, ecutrho =600,
occupations='smearing', smearing='methfessel-paxton', degauss=0.04,
la2F = .true.,
/
&electrons
conv_thr =  1.0d-8
mixing_beta = 0.7
/
&IONS
/
&CELL
  press = 0.0
  cell_factor = 1.5d0
/
ATOMIC_SPECIES
Mg 24.305 Mg.pw91-np-van.UPF
B  10.811 B.pw91-n-van_ak.UPF
ATOMIC_POSITIONS {crystal}
Mg  0.000000000       0.000000000       0.000000000
B 0.333333333       0.666666667       0.500000000
B 0.666666667       0.333333333       0.500000000
K_POINTS {automatic}
32 32 32 0 0 0
EOF
$ECHO "  running the scf calculation with dense k-point grid...\c"
$PW_COMMAND  < mgb2.scf.fit.in > mgb2.scf.fit.out
check_failure $?
$ECHO "  done"
#
#  SCF at k-mesh good enough for phonons
#
cat > mgb2.scf.in << EOF
&control
calculation='scf'
restart_mode='from_scratch',
prefix='mgb2',
etot_conv_thr = 1.0d-8
forc_conv_thr = 1.0d-7
pseudo_dir = '$PSEUDO_DIR/',
outdir='$TMP_DIR/'
/
&system
ibrav=  4, celldm(1) =5.8124, celldm(3)=1.1483, nat= 3, ntyp= 2,
ecutwfc = 60.0,ecutrho = 600,
occupations='smearing', smearing='methfessel-paxton', degauss=0.04
/
&electrons
conv_thr =  1.0d-8
mixing_beta = 0.7
/
&IONS
/
&CELL
  press = 0.0
  cell_factor = 1.5d0
/
ATOMIC_SPECIES
Mg 24.305 Mg.pw91-np-van.UPF
B  10.811 B.pw91-n-van_ak.UPF
ATOMIC_POSITIONS {crystal}
Mg  0.000000000       0.000000000       0.000000000
B 0.333333333       0.666666667       0.500000000
B 0.666666667       0.333333333       0.500000000
K_POINTS {automatic}
  16 16 16  0 0 0
EOF
$ECHO "  running the scf calculation...\c"
$PW_COMMAND < mgb2.scf.in > mgb2.scf.out
check_failure $?
$ECHO "  done"
#
cat > mgb2.elph.in << EOF
Electron-phonon coefficients for LiCs
&inputph
  iverbosity=1
  tr2_ph=1.0d-12,
  prefix='mgb2',
  fildvscf='mgb2dv',
  amass(1)=24.305,
  amass(2)=10.811,
  outdir='$TMP_DIR/',
  fildyn='mgb2.dyn',
  electron_phonon='interpolated',
  trans=.true.,
  ldisp=.true.
  nq1=8, nq2=8, nq3=8
/
EOF
$ECHO "  running the el-ph calculation...\c"
$PH_COMMAND < mgb2.elph.in > mgb2.elph.out
check_failure $?
$ECHO "  done"
#
# q2r and matdyn
#
cat > q2r.in << EOF
&input
  zasr='simple',  fildyn='mgb2.dyn', flfrc='mgb2.fc', la2F=.true.
/
EOF
$ECHO "  running q2r...\c"
$Q2R_COMMAND < q2r.in > q2r.out
check_failure $?
$ECHO "  done"
#
#
#
cat > matdyn.in.freq << EOF
&input
asr='simple',  amass(1)=24.305, amass(2)=10.811,
flfrc='mgb2.fc', flfrq='mgb2.freq', la2F=.true., dos=.false.
/
  19
  0.000 0.0 0.0    0.0
  0.125 0.0 0.0    0.0
  0.250 0.0 0.0    0.0
  0.375 0.0 0.0    0.0
  0.500 0.0 0.0    0.0
  0.750 0.0 0.0    0.0
  1.000 0.0 0.0    0.0
  0.825 0.125 0.125 0.0
  0.750 0.250 0.250 0.0
  0.625 0.375 0.375 0.0
  0.500 0.500 0.500 0.0
  0.325 0.325 0.325 0.0
  0.250 0.250 0.250 0.0
  0.125 0.125 0.125 0.0
  0.000 0.000 0.000 0.0
  0.125 0.125 0.000 0.0
  0.250 0.250 0.000 0.0
  0.325 0.325 0.000 0.0
  0.500 0.500 0.000 0.0
EOF
$ECHO "  running matdyn for frequency calculation...\c"
$MATDYN_COMMAND < matdyn.in.freq > matdyn.out.freq
check_failure $?
$ECHO "  done"
#
#
#
cat > matdyn.in.dos << EOF
&input
asr='simple',  amass(1)=24.305, amass(2)=10.811,
flfrc='mgb2.fc', flfrq='mgb2.freq', la2F=.true., dos=.true.
fldos='phonon.dos', nk1=10, nk2=10, nk3=10, ndos=50
/
EOF
$ECHO "  running matdyn for a2F(omega) calculation...\c"
$MATDYN_COMMAND < matdyn.in.dos > matdyn.out.dos
check_failure $?
$ECHO "  done"
#
#
#
cat > lambda.in << EOF
50  0.05  1 ! emax (something more than highest phonon mode in THz), degauss, smearing method
1       ! Number of q-points for which EPC is calculated,                                                                                        /其余的q点会在计算Tc是加上。
   0.000000  0.000000  0.000000 1
elph. 0.000000. 0.000000. 0.000000
0.10                   ! \mu the Coloumb coefficient in the modified
                     ! Allen-Dynes formula for T_c (via \omega_log)
EOF
$ECHO "  running lambda.x for lambda calculation...\c"
$LAMBDA_COMMAND < lambda.in > lambda.out
check_failure $?
$ECHO "  done"

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1楼 2014-05-14 08:52:14

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ccmin4

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什么是cell_factor?

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2楼2014-05-28 13:47:00

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flying_lw

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引用回帖:

2楼: Originally posted by ccmin4 at 2014-05-28 13:47:00
什么是cell_factor?

cell_factor:
Used in the construction of the pseudopotential tables.
It should exceed the maximum linear contraction of the
cell during a simulation.

这是QE网站上关于输入参数的介绍。具体的我也不是特别理解。

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3楼2014-06-24 07:32:39

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楼主解决了吗，我也遇到这个问题了，celldm(3)=1.1483这个值对不对，文献中写的c轴晶格常数是3.524艾，那celldm(3)就应该是6.65939438，但是我看好多关于MgB2的例子中celldm(3)都是等于1.1483，不知道是不是我想错了

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