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Hi, can someone please look at my output and tell me if the calculation is right or wrong. I think acell of MgB2 should be around a=5.85Bohr, but from my calculation i got 6.0Bohr.
-outvars: echo values of variables after computation --------
acell1 5.2280332760E+00 5.2280332760E+00 5.2280332760E+00 Bohr
acell2 5.3280332760E+00 5.3280332760E+00 5.3280332760E+00 Bohr
acell3 5.4280332760E+00 5.4280332760E+00 5.4280332760E+00 Bohr
acell4 5.5280332760E+00 5.5280332760E+00 5.5280332760E+00 Bohr
acell5 5.6280332760E+00 5.6280332760E+00 5.6280332760E+00 Bohr
acell6 5.7280332760E+00 5.7280332760E+00 5.7280332760E+00 Bohr
acell7 5.8280332760E+00 5.8280332760E+00 5.8280332760E+00 Bohr
acell8 5.9280332760E+00 5.9280332760E+00 5.9280332760E+00 Bohr
acell9 6.0280332760E+00 6.0280332760E+00 6.0280332760E+00 Bohr
acell10 6.1280332760E+00 6.1280332760E+00 6.1280332760E+00 Bohr
acell11 6.2280332760E+00 6.2280332760E+00 6.2280332760E+00 Bohr
acell12 6.3280332760E+00 6.3280332760E+00 6.3280332760E+00 Bohr
amu 2.43050000E+01 1.08110000E+01
ecut 5.00000000E+01 Hartree
ecutsm 5.00000000E-01 Hartree
etotal1 -8.0755963150E+00
etotal2 -8.1058161310E+00
etotal3 -8.1301618737E+00
etotal4 -8.1493217604E+00
etotal5 -8.1639036632E+00
etotal6 -8.1744439819E+00
etotal7 -8.1814125642E+00
etotal8 -8.1852365910E+00
etotal9 -8.1862918823E+00
etotal10 -8.1849170811E+00
etotal11 -8.1814149440E+00
etotal12 -8.1760351470E+00
fcart1 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -1.5590142420E-23 1.6533972948E-39
-0.0000000000E+00 1.5590142420E-23 -1.6533972948E-39
fcart2 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -1.5297536470E-23 1.6223652571E-39
-0.0000000000E+00 1.5297536470E-23 -1.6223652571E-39
fcart3 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
fcart4 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
fcart5 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
fcart6 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -1.7786598695E-24 1.8863403151E-40
-0.0000000000E+00 1.7786598695E-24 -1.8863403151E-40
fcart7 -0.0000000000E+00 -1.8646835503E-23 1.9775718878E-39
-0.0000000000E+00 9.3234177514E-24 -9.8878594390E-40
-0.0000000000E+00 9.3234177514E-24 -9.8878594390E-40
fcart8 -0.0000000000E+00 3.6664564027E-23 -3.8884244508E-39
-0.0000000000E+00 9.1661410068E-24 -9.7210611270E-40
-0.0000000000E+00 -4.5830705034E-23 4.8605305635E-39
fcart9 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -1.0816898928E-22 1.1471756283E-38
-0.0000000000E+00 1.0816898928E-22 -1.1471756283E-38
fcart10 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 5.3201919559E-23 -5.6422775051E-39
-0.0000000000E+00 -5.3201919559E-23 5.6422775051E-39
fcart11 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
fcart12 -0.0000000000E+00 -0.0000000000E+00 -0.0000000000E+00
-0.0000000000E+00 -8.0500705943E-25 8.5374235750E-41
-0.0000000000E+00 8.0500705943E-25 -8.5374235750E-41
getwfk -1

You should do the calculation using optcell, see Tutorial 3, it's much easier and more reliable. Secondly, it's typically unexpected to get relaxed lattice parameters that match experiment, because the exchange correlation models are imperfect. LDA typically gives relaxed cells 1-3% smaller than experiment, while GGA models like PBE typically give 1-3% larger than experiment.

Josef W. Zwanziger thanks for usual assistance.

Dear Jzwanzig,
please help me out. I am working on cubic system and i have the following output

"Scale of Primitive Cell (acell) [bohr]
8.80000000000000E+00 8.80000000000000E+00 8.80000000000000E+00
Real space primitive translations (rprimd) [bohr]
0.00000000000000E+00 4.40000000000000E+00 4.40000000000000E+00
4.40000000000000E+00 0.00000000000000E+00 4.40000000000000E+00
4.40000000000000E+00 4.40000000000000E+00 0.00000000000000E+00
Unitary Cell Volume (ucvol) [Bohr^3]= 1.70368000000000E+02
Angles (23,13,12)= [degrees]
6.00000000000000E+01 6.00000000000000E+01 6.00000000000000E+01
Lengths [Bohr]
6.22253967444162E+00 6.22253967444162E+00 6.22253967444162E+00
Stress tensor in cartesian coordinates (strten) [Ha/bohr^3]
-9.31428390291595E-04 0.00000000000000E+00 0.00000000000000E+00
0.00000000000000E+00 -9.31428390291594E-04 0.00000000000000E+00
0.00000000000000E+00 0.00000000000000E+00 -9.31428390291593E-04
Total energy (etotal) [Ha]= -1.18290446959563E+01


Cartesian components of stress tensor (hartree/bohr^3)
sigma(1 1)= -9.31428390E-04 sigma(3 2)= 0.00000000E+00
sigma(2 2)= -9.31428390E-04 sigma(3 1)= 0.00000000E+00
sigma(3 3)= -9.31428390E-04 sigma(2 1)= 0.00000000E+00

-Cartesian components of stress tensor (GPa) [Pressure= 2.7404E+01 GPa]
- sigma(1 1)= -2.74035647E+01 sigma(3 2)= 0.00000000E+00
- sigma(2 2)= -2.74035647E+01 sigma(3 1)= 0.00000000E+00
- sigma(3 3)= -2.74035647E+01 sigma(2 1)= 0.00000000E+00"

I don't know values to pick from this output to calculate bulk modulus and pressure derivative of bulk modulus.
Thanks

Dear Mr BAMGBOSE, M. K.
It would be very beneficial if you presented us the input file. cordially ...