[Thermo_pw-forum] Need Assistance for calculation of elastic constants using Thermo_Pw code

[heena khan]

Dear Developers/Users,

 My name is Heena, and I am currently a beginner in the field of using the
Thermo PW code for elastic constant determination. I am working on
perovskite of type A2BB'X5, which is stable in the tetragonal phase.
I have encountered an issue in my calculations. While employing the Thermo
PW code, I find that it generates seven elastic constants(Cij) instead of
the six(Cij) (expected for tetragonal structure). below, I mention the
obtained elastic constants for the same.
I am reaching out to seek guidance or assistance from anyone who may have
experience with this code or a similar situation. It would be immensely
grateful.


Elastic constants C_ij (kbar)
    i j=        1           2           3           4           5
6
    1   234.09216    54.10432   122.15608     0.00000     0.00000
0.00000
    2    54.10432   234.09216   122.15608     0.00000     0.00000
0.00000
    3   127.14759   127.14759   346.94234     0.00000     0.00000
0.00000
    4     0.00000     0.00000     0.00000    62.34926     0.00000
0.00000
    5     0.00000     0.00000     0.00000     0.00000    62.34926
0.00000
    6     0.00000     0.00000     0.00000     0.00000     0.00000
 85.50041

     1 bar = 10^5 Pa; 10 kbar = 1 GPa; 1 atm = 1.01325 bar; 1 Pa = 1 N/m^2
     1 Pa = 10 dyn/cm^2; 1 Mbar = 10^11 Pa
     1 torr = 1 mm Hg = 1/760 bar = 7.5006 x 10^-3 Pa
                    ----------------------------------------

     Elastic compliances  S_ij (1/Mbar)
    i j=        1           2           3           4           5
6
    1     5.29482    -0.26111    -1.77233     0.00000     0.00000
0.00000
    2    -0.26111     5.29482    -1.77233     0.00000     0.00000
0.00000
    3    -1.84475    -1.84475     4.18137     0.00000     0.00000
0.00000
    4     0.00000     0.00000     0.00000    16.03868     0.00000
0.00000
    5     0.00000     0.00000     0.00000     0.00000    16.03868
0.00000
    6     0.00000     0.00000     0.00000     0.00000     0.00000
 11.69585

Thank you for your time and consideration.--
Heena
Research scholar
JMI
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