[QE-users] How ev.x calculate enthalpy?

[Inna Nangoi]

Dear Stefano, thank you for your answer.


Converting the values I get:

2.93 GPa = 29.3 kbar (Ry/Bohr^3)

120.51 A^3 = 813.24 Bohr^3

P*V = 23827.932 Ry

E(fit) = -181.23269 Ry

enthalpy = -181.23269+23827.932 =23646,70536041 Ry


It is something very stupid that I can't see where am I doing wrong.


Another question is regarding the chisq , what should be a reasonable value?


Best

Inna


________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Stefano de Gironcoli <degironc at sissa.it>
Sent: 08 May 2020 09:29:58
To: users at lists.quantum-espresso.org
Subject: Re: [QE-users] How ev.x calculate enthalpy?


dear Inna,


  in the output file energies and enthalpies are written in Ry, volumes in A^3 and pressures in GPa

  in order to apply directly the enthalpy formula everything should be given with consistent units.

  if you check the ev.f90 code (in PW/tools) there are unit conversion factors when using the pressure


line 304:         epv(i) = etot(i) + p(i)*v0(i) / ry_kbar


   and when printing the volume


lines 350-352:

          WRITE(iun,'(f8.2,2x,f12.5, 2x,f12.5, f12.5, 3x, f8.2, 3x,f12.5)') &
              ( v0(i)*bohr_radius_angs**3, etot(i), efit(i),  &
               etot(i)-efit(i), p(i)/gpa_kbar, epv(i), i=1,npt )


   best


stefano


On 08/05/20 09:01, Inna Nangoi wrote:
Hi,
I can't figure out how ev.x calculate enthalpy. I checked the ev.f90 and found out that
Enth(i)=Efit(i)+Pfit(i)*V0(i) is the enthalpy (Ry)
But when I try to calculate by hand I don't reach the same value as reported in ev.x
output file (see below) . For example, for V = 120.51
Enth(i)=Efit(i)+Pfit(i)*V0(i)
Enth(i)= -181.23265  + 2.93*120.51 = 171.86161

What am I doing wrong?

# equation of state: murnaghan.        chisq =   0.4329D-07
# V0 =  996.51 a.u.^3,  k0 =   92 kbar,  dk0 =  4.10  d2k0 =  0.000  emin = -181.24780
# V0 =  147.67  Ang^3,  k0 =   9.2 GPa

##########################################################################
# Vol.        E_calc        E_fit       E_diff    Pressure      Enthalpy
# Ang^3         Ry           Ry            Ry        GPa           Ry
##########################################################################
  124.13    -181.23698    -181.23704     0.00005       2.34     -181.10397
  120.51    -181.23265    -181.23269     0.00003       2.93     -181.07085

Best
Inna Nangoi
Stockholm University /Universidade Federal de Juiz de Fora




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