[Pw_forum] problem of the second derivative of energy of DFPT
贺伟
weihe at mail.ustc.edu.cn
Wed Jan 7 12:54:33 CET 2004
Dear PWSCF user
I want to get the second derivatives of Born-Oppenheimer energy surface,
but I found that dinsity functional perturbation mothod gave different result
than the stupid finite difference method.
My testing system is the AlAs bulk. In finite difference method, I first
did a scf calculation with the relaxed geometry. Then I moved Al atom 1/1000
of celldm(1) along x and -x directions, and did scf calculations again. The
resulting three energies gave a FD second derivative of energy as 0.571 Ryd/Bohr^2.
But DFTP gave the second derivative as 0.203 Ryd/Bohr^2 (the first element of
the dynamic matrix).
Can anybody give me some suggestion? Thanks! I have attach the input files
with this email.
Best Wishes
Wei He
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