[QE-users] Bulk modulus and Total energy MgH2

[Paolo Giannozzi]

On 02/09/2024 17:32, RAQUEL YANES RODRIGUEZ wrote:

> it appears that B0 should be around 40-50 GPa. However, I am obtaining a 
> value of 5 GPa

> The obtained values of volume (where V=a^2*c) and total energy are:
> 
> Vol (ang^3)  Total energy (eV)
> 28.640500    -89.84334
> 33.836204    -89.93096
> 36.654496    -89.95390
> 39.625092    -89.96478
> 42.752000    -89.96531
> 46.039228    -89.95738
> 49.490784    -89.94272
> 56.902912    -89.89999
> 65.020448    -89.84715

So, I put those numbers into a file mgh2.dat and run ~/q-e/bin/ev.x:

      Lattice parameter or Volume are in (au, Ang) > Ang
      Assuming Angstrom
      Enter type of bravais lattice (fcc, bcc, sc, noncubic) > noncubic
      Enter type of equation of state :
      1=birch1, 2=birch2, 3=keane, 4=murnaghan > 4
      Input file > mgh2.dat
  Minimization succeeded
      Output file > mgh2.dat
      Beware: file mgh2.dat will be overwritten

The contents of file 'mgh2.dat':

# equation of state: murnaghan.        chisq =   0.1905D-05
# V0 =  278.49 a.u.^3,  k0 =  745 kbar,  dk0 =  3.76  d2k0 =  0.000 
emin =  -89.96467
# V0 =   41.27  Ang^3,  k0 =  74.6 GPa

##########################################################################
# Vol.        E_calc        E_fit       E_diff    Pressure      Enthalpy
# Ang^3         Ry           Ry            Ry        GPa           Ry
##########################################################################
    28.64     -89.84334     -89.84281    -0.00053      58.46      -89.07520
    33.84     -89.93096     -89.93301     0.00205      22.01      -89.58937
    36.65     -89.95390     -89.95399     0.00009      11.14      -89.76660
    39.63     -89.96478     -89.96348    -0.00130       3.27      -89.90528
    42.75     -89.96531     -89.96381    -0.00150      -2.47      -90.01369
    46.04     -89.95738     -89.95672    -0.00066      -6.69      -90.09865
    49.49     -89.94272     -89.94351     0.00079      -9.82      -90.16562
    56.90     -89.89999     -89.90241     0.00242     -13.91      -90.26305
    65.02     -89.84715     -89.84580    -0.00135     -16.25      -90.33175

The bulk modulus (k0) seems to be around 75 GPa

> According to literature, the total energy should be around -17.822 eV 

The total energy in a pseudopotential calculation depends upon the 
pseudopotential

Paolo

> after optimization. However, my values are around -89 eV (-6.61 Ry). I 
> cannot find where the problem lies. I have verified that ecutwfc, 
> ecutrho, and the k-points are converged. I can’t think of what else to 
> do. Could someone please verify the total energy of this structure or 
> guide me on where the issue might be?
> 
> Thank you in advance!

-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
X SCUOLA ENERGIE RINNOVABILI 16-21/9/2024 - PRE-ISCRIZIONE 
https://agenda.infn.it/event/39573/