Enthalpy

2023/10/18

Info

Requirements:

  • CrySPY 1.2.2 or later
  • VASP or QE

When performing CSP at high pressure, enthalpy results can be collected instead of total energy. Not yet compatible with softwares other than VASP and QE.

E_eV_atom in cryspy_rslt and cryspy_rslt_energy_asc turns into enthalpy (eV/atom). Here is the example of CSP results under 40 GPa pressure for Sr4O4. CsCl-type structure (ID 5) is more stable than NaCl-type (ID 6).

   Spg_num Spg_sym  Spg_num_opt Spg_sym_opt  E_eV_atom  Magmom      Opt
5       26  Pmc2_1          221       Pm-3m  -2.276790     NaN     done
6      225   Fm-3m          225       Fm-3m  -2.244800     NaN     done
1      101  P4_2cm          107        I4mm  -2.181115     NaN     done
4      123  P4/mmm          123      P4/mmm  -2.034509     NaN  not_yet
3       20  C222_1           63        Cmcm  -0.686541     NaN     done
2       75      P4           75          P4  -0.008713     NaN  not_yet
9       51    Pmma           47        Pmmm   0.096430     NaN     done
8       65    Cmmm          123      P4/mmm   1.099657     NaN     done
0      187   P-6m2          187       P-6m2   1.292124     NaN     done
7       53    Pmna           53        Pmna   5.153504     NaN  not_yet

VASP

CrySPY reads energy (enthalpy) from a OSZICAR file. This automatically changes to enthalpy when PSTRESS is set in INCAR_x as follows:

PSTRESS = 400

You do not have to do anything in cryspy.in. energy_step_flag is also supported for enthalpy.

Example: CrySPY utility > examples > qe_Sr4O4_RS_pv_term

QE

Add pv_term = True in the QE section of cryspy.in to use enthalpy:

[QE]
qe_infile = pwscf.in
qe_outfile = pwscf.out
kppvol =  40  80
pv_term = True

Don’t forget to write press in the QE input:

 &cell
    press = 400
 /
Warning

In QE, energy_step_flag is not supported yet for enthalpy.