ELPH_IGNORE_IMAG_PHONONS

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ELPH_IGNORE_IMAG_PHONONS = .TRUE. | .FALSE.
Default: ELPH_IGNORE_IMAG_PHONONS = .FALSE. 

Description: If enabled, VASP ignores imaginary phonon frequencies during electron-phonon calculations.

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Imaginary phonon frequencies are often a sign that the system in question is not well-converged or not well-described by the simulation. In this case, the system should first be properly converged until stable (real) phonons are obtained.

Mind: Imaginary phonon frequencies can also appear at phase transitions or other lattice instabilities. However, for perturbative electron-phonon calculations, you should always choose a stable equilibrium structure.

If imaginary phonon frequencies are encountered during an electron-phonon calculation, VASP simply stops. If ELPH_IGNORE_IMAG_PHONONS = True, VASP instead skips the q-points at which the phonon frequencies are imaginary. This can be useful since even a stable system can sometimes exhibit small imaginary phonon frequencies around the $\Gamma$-point due to numerical inaccuracies.