[Pw_forum] Problem with band structure computation

jchuang jchuang at pub.iams.sinica.edu.tw
Tue Aug 30 08:57:14 CEST 2011


Dear all,

 

I've got a problem when computing the band structure for mono-layer CaC6.

The paper I followed is here (Arxiv preprint arXiv:1105.3736, 2011 -
arxiv.org).

They got their results from QE, too.

 

The problem is not about QE running process. It's about the result I got
from QE simulation.

 

If I set the parameters (atomic positions and celldm) as the same as paper.

The band structure I got was different from paper.

Some bands are fine, but some are distorted.

For example, part of a band with flat shape be tilted.

The link for my result is here. (http://imgur.com/fUSna)

 

It looks like something wrong with my atomic structure.

But it isn't. I had examined the atomic structure and k-path for many times.

 

To check the validity of atomic positions. I also tried the same structure
with VASP.

The result from VASP could fit the paper pretty well.

 

To check the validity of input files for QE. (parameters and k-path)

I tried to plot the band structure of mono-layer LiC6 with QE.

The band structure of LiC6 could fit the paper, too.

 

I had tried to relax the structure or use other pseudo potential files, but
still none better.

 

Why I use the correct structure and correct input files, but couldn't get a
correct result?

Have there been any wrong in my input setting?

 

Could someone please give me any advices or clues?

Any suggestions will be greatly appreciated.

 

Best regards,

 

J. C. Huang  IAMS, Taiwan

 

================= the following is my input files =================

 

Scf.in

&control

    calculation ='scf'

    restart_mode ='from_scratch'

    pseudo_dir ='/lustre/lwork/dyyang/bin/espresso-4.0.3/pseudo/'

    outdir ='./'

    prefix ='AuC'

    disk_io='low',

    wf_collect=.TRUE.,

 /

 &system

    ibrav = 4,

    celldm(1) = 8.050232711,

    celldm(3) = 4.694835681,

    nat = 7,

    ntyp = 2,

    ecutwfc = 45,

    ecutrho = 400,

    occupations = "smearing",

    smearing   = 'gaussian'

    degauss    = 0.002D0

 /

 &electrons

    diagonalization='david'

    mixing_mode = 'plain'

    conv_thr = 1.0e-08

    mixing_beta = 0.7

 /

 &ions

    bfgs_ndim = 3,

ATOMIC_SPECIES

  Ca 40.08 Ca.pz-n-vbc.UPF

  C 12.0107 C.pz-vbc.UPF

ATOMIC_POSITIONS {crystal}

 Ca    0.66667    0.33333    0.61200

 C     0.33333    0.00000    0.50000

 C     0.33333    0.33333    0.50000

 C     0.00000    0.33333    0.50000

 C     0.00000    0.66667    0.50000

 C     0.66667    0.66667    0.50000

 C     0.66667    0.00000    0.50000

K_POINTS (automatic)

16 16 1 0 0 0 

 

Band1.in

# self-consistent calculation

 &control

    calculation='bands',

    restart_mode='from_scratch',

    prefix='AuC',

    pseudo_dir = '/lustre/lwork/dyyang/bin/espresso-4.0.3/pseudo/',

    outdir='./'

    tstress = .true.

    tprnfor = .true.

    forc_conv_thr = 1.0e-3

 /

 &system

    ibrav = 4,

    celldm(1) = 8.050232711,

    celldm(3) = 4.694835681,

    nat=7, ntyp=2

    ecutwfc =45.0,

    ecutrho =400,

    occupations = "smearing",

    smearing    = "gaussian",

    degauss     = 0.002D0,

    nbnd= 20

/

 &electrons

    diagonalization='david'

    mixing_mode = 'plain'

    mixing_beta = 0.7

    conv_thr =  1.0e-8

/

 &ions

    bfgs_ndim = 3,

ATOMIC_SPECIES

  Ca 40.08 Ca.pz-n-vbc.UPF

  C 12.0107 C.pz-vbc.UPF

ATOMIC_POSITIONS {crystal}

 Ca    0.66667    0.33333    0.61200

 C     0.33333    0.00000    0.50000

 C     0.33333    0.33333    0.50000

 C     0.00000    0.33333    0.50000

 C     0.00000    0.66667    0.50000

 C     0.66667    0.66667    0.50000

 C     0.66667    0.00000    0.50000

K_POINTS {crystal}

49

  0.00000000  0.00000000  0.00000000    1

  0.03125000  0.00000000  0.00000000    2

  0.06250000  0.00000000  0.00000000    3

  0.09375000  0.00000000  0.00000000    4

  0.12500000  0.00000000  0.00000000    5

  0.15625000  0.00000000  0.00000000    6

  0.18750000  0.00000000  0.00000000    7

  0.21875000  0.00000000  0.00000000    8

  0.25000000  0.00000000  0.00000000    9

  0.28125000  0.00000000  0.00000000   10

  0.31250000  0.00000000  0.00000000   11

  0.34375000  0.00000000  0.00000000   12

  0.37500000  0.00000000  0.00000000   13

  0.40625000  0.00000000  0.00000000   14

  0.43750000  0.00000000  0.00000000   15

  0.46875000  0.00000000  0.00000000   16

  0.50000000  0.00000000  0.00000000   17

  0.48958333  0.02083333  0.00000000   18

  0.47916666  0.04166666  0.00000000   19

  0.46874999  0.06249999  0.00000000   20

  0.45833333  0.08333332  0.00000000   21

  0.44791666  0.10416666  0.00000000   22

  0.43749999  0.12499999  0.00000000   23

  0.42708332  0.14583332  0.00000000   24

  0.41666665  0.16666665  0.00000000   25

  0.40624998  0.18749998  0.00000000   26

  0.39583331  0.20833331  0.00000000   27

  0.38541664  0.22916664  0.00000000   28

  0.37499997  0.24999997  0.00000000   29

  0.36458331  0.27083331  0.00000000   30

  0.35416664  0.29166664  0.00000000   31

  0.34374997  0.31249997  0.00000000   32

  0.33333330  0.33333330  0.00000000   33

  0.31249997  0.31249997  0.00000000   34

  0.29166664  0.29166664  0.00000000   35

  0.27083331  0.27083331  0.00000000   36

  0.24999997  0.24999997  0.00000000   37

  0.22916664  0.22916664  0.00000000   38

  0.20833331  0.20833331  0.00000000   39

  0.18749998  0.18749998  0.00000000   40

  0.16666665  0.16666665  0.00000000   41

  0.14583332  0.14583332  0.00000000   42

  0.12499999  0.12499999  0.00000000   43

  0.10416666  0.10416666  0.00000000   44

  0.08333333  0.08333333  0.00000000   45

  0.06249999  0.06249999  0.00000000   46

  0.04166666  0.04166666  0.00000000   47

  0.02083333  0.02083333  0.00000000   48

  0.00000000  0.00000000  0.00000000   49

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