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

[Stefano de Gironcoli]

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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