# [Pw_forum] units of psi in e-ph coupling matrix element

Paolo Giannozzi giannozz at democritos.it
Fri Feb 24 09:08:13 CET 2012

On Thu, 2012-02-23 at 17:08 -0500, Ajit Vallabhaneni wrote:

> I am familiar with the equation (1) in that file.
> However, it is still not clear to me how does 'g'
> has the units of energy (eV or Ry).

the multiplying factor has the dimension of a length,
the matrix element of an energy over a length

>  Is the wave function psi considered unitless ?

no: \int \psi^* \psi dV is adimensional.

P.
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Paolo Giannozzi, IOM-Democritos and University of Udine, Italy