Dear all, I am trying to calculate the bulk modulus of single crystal Pentacene which has a triclinic unit cell with 72 atoms. Starting from an optimized structure, with ibrav = 14 (corresponding to triclinc structure), I performed a series of SCF calculations. I changed one of the lattice constants by modifying celldm(1), celldm(2) and celldm(3) appropriately. I then used ev.x to extract the bulk modulus (with the non-cubic option). I also tried to calculate it directly from the parabolic fitting of energy vs volume.
>From both approaches, I am getting a bulk modulus ~ 350 GPa, which seems unrealistic. I have verified that I am able to get the right value of the Bulk modulus for Silicon using both approaches. I was wondering if there is a different way to go about calculating bulk modulus values for triclinic structure, or if there is something wrong about the way I have set up my input files. I have attached my input files for two different configurations, the equilibrium lattice constant and the strained value where celldm(1) = a, has been changed by 5%. I would really appreciate some help with this. Thanks, Varsha Rani PhD student School of Physical Sciences Jawaharlal Nehru University, New Delhi, India
penta.scf-relaxd-min5a-axis-vdW-DF-ecut-40.in
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penta.scf-relaxd-plus5-a-axis-vdW-DF-ecut-40.in
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