Hello Antoine, Your procedure does not look obviously wrong to me, but you did not say what X is.
-- Lorenzo Paulatto Written on a virtual keyboard with real fingers On Sat, 14 Jul 2018, 10:43 JAY Antoine, <[email protected]> wrote: > Dear all, > I would like to (re)obtain the phonons frequencies that I first obtained > using DFPT but from finite difference. > > Lets be R0 the ground state atomic positions and U the normalised atomic > displacement of a normal mode obtained from DFPT. > I have calculated the total energy from DFT of 11 structures R0+i*0.01*U > with i variing from -5 to 5. The so obtained curve is fitted with a second > order polynom a0+a1*X+a2*X^2, so that I obtain the second order derivative > of the total energy with respect to the atomic displacements of the studied > mode: 2*a2. I then divided by the atomic mass (one type of mass) and I > should obtain the omega^2, but my resulting value is 3 or four times to big. > > I use a cubic supercell with one type of atom. > > Did someone already performed this kind of work? > How should I do with differents atomic masses? > > Thank you very much for your help, > > Antoine Jay > > > > _______________________________________________ > users mailing list > [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users
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