How to calculate Elastic constants using THERMO

This example computes the elastic constants of silicon at the minimum of the Murnaghan equation. The atoms are relaxed for e44 strains.

To install the THERMO_PW package click on the following link:

How to install and use the THERMO_PW package

To calculate the band structure ( example13 ) we need 2 input files and a pseudopotentia

si.elastic.in

 &control
    calculation = 'scf'
    restart_mode='from_scratch',
    prefix='silicon',
    pseudo_dir = '/home/algerien/abinitio/q-e-qe-6.8/pseudo/',
    outdir='/home/algerien/abinitio/q-e-qe-6.8/tempdir/'
 /
 &system
    ibrav=  2, 
    celldm(1) =10.20, 
    nat= 2, 
    ntyp= 1,
    ecutwfc=24.0,
 /
 &electrons
    conv_thr =  1.0d-8
 /
ATOMIC_SPECIES
 Si  28.086  Si.pz-vbc.UPF
ATOMIC_POSITIONS (alat)
 Si 0.00 0.00 0.00
 Si 0.25 0.25 0.25
K_POINTS AUTOMATIC
4 4 4 1 1 1

thermo_control

 &INPUT_THERMO
  what='mur_lc_elastic_constants',
  frozen_ions=.FALSE.
 /

Si.pz-vbc.UPF It's better to download the file in the pseudo directory $QEROOT/pseudo

You can download the file using the following command

$ cd $QEROOT/pseudo
algerien1970@linux-ml0a:~/abinitio/q-e-qe-6.8/pseudo>
wget https://www.quantum-espresso.org/upf_files/Si.pz-vbc.UPF --no-check-certifica

We do the calculation using the following command

algerien1970@linux-ml0a:~/abinitio/QE-tutorials/thermo-examples/Si_Elastic>
thermo_pw.x < si.elastic.in |tee si.elastic.out

We list the contents of ouput

algerien1970@linux-ml0a:~/abinitio/QE-tutorials/thermo-examples/Si_Elastic> ls
elastic_constants  energy_files  gnuplot_files  output_mur.ps  output_therm_debye.dw.g1.ps

output_therm_debye.g1.ps  restart  si.elastic.in  si.elastic.out  therm_files  thermo_control

The output graphs are in fileoutput_mur.ps output_therm_debye.dw.g1.ps output_therm_debye.g1.ps which we have converted it to jpg files

The content of output_ev.dat.ev.out is as follows:

# equation of state: murnaghan.        chisq = 0.6979D-10
# V0 =  266.30 a.u.^3,  k0 =  944 kbar,  dk0 =  4.09  d2k0 =  0.000  emin =  -15.85083
# V0 =   39.46  Ang^3,  k0 =  94.4 GPa

##########################################################################
# Vol.        E_calc        E_fit       E_diff    Pressure      Enthalpy
# a.u.^3        Ry           Ry            Ry        GPa           Ry
##########################################################################
  250.00     -15.84726     -15.84726     0.00000       6.81      -15.73159
  253.77     -15.84879     -15.84878    -0.00001       5.03      -15.76199
  257.58     -15.84985     -15.84986     0.00002       3.37      -15.79083
  261.42     -15.85055     -15.85054    -0.00001       1.82      -15.81829
  265.30     -15.85082     -15.85082     0.00000       0.36      -15.84436
  269.22     -15.85073     -15.85073     0.00000      -1.01      -15.86916
  273.18     -15.85029     -15.85029    -0.00000      -2.29      -15.89275
  277.18     -15.84951     -15.84950    -0.00001      -3.49      -15.91520
  281.22     -15.84838     -15.84839     0.00000      -4.61      -15.93655