I have a question concerning with the calculation of pressure for the transition
metals.
I carried out a series of calculations for the three metals, using dataset on
parameter tsmear, that in the chosen smearing method (Fermi-Dirac smearing) has
the meaning of the electron temperature. For each metal (there were 3)
three calculation was conducted on a grid of the electron temperature.
At the first calculation the value of the lattice constant acell have been set so that
the pressure is equal to zero as the tsmear vanishes to "zero"(~300K). In the second
and in the third case, the lattice constant decreased or increased by the same order
of magnitude, so that the change in volume is 10%.
After that I decided to compare the pressure that is written in the output file
with the total energy change to volume change ratio with the opposite sign.
I used obtained data for energies in the following way:
P(from total energy)=-(E_total(V+dV)-E_total(V-dV))/2dV.
For Aluminum (simple metal) and Gold (noble metal) results are in good agreement.
The results of such comparison for Nickel were quite strange. In the case of Nickel
the band energy change to volume change ratio is close to the value of pressure
in output file. The total energy change to the volume change ratio
(with opposite sign) is less than the displayed pressure approximately on 60 GPa at 55000K.
What could be wrong in the calculation for the thermodynamic properties of nickel?
Example of typical input file
Nid2v-.in- reduced volume and Te from 17500K to 55000K
- (1.95 KiB) Downloaded 316 times
The table with comparison of pressure dependence on electron temperature are
placed in the attached archive. All values of pressure are given in GPa.
"T, K" "dEbands/dV" "P"
1000 0 0.49036
2000 0.68821440721487 1.457
4000 2.3948711866606 4.311
5000 3.5939891506768 6.1755
7500 8.1118806847963 11.737
10000 14.504710603589 18.039
12500 22.043931332789 24.68
15000 30.219045797126 31.546
17500 38.781721498029 38.669
20000 46.539388712704 45.208
22500 55.564749922761 52.999
25000 64.785367853599 61.198
30000 83.690507054404 78.805
37500 112.75841141436 107.77
45000 141.82442706816 138.92
55000 179.23035053145 182.65
With regards, Kirill Migdal.