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

[Ajit Vallabhaneni]

Dear users and developers,

           The e-ph coupling matrix element (g) has the units of 'energy (eV or Ry)' in the literature. But from the expression for calculating the e-ph coupling matrix element, i obtained the unit of 'energy per unit volume' for g assuming the term psi has the unit of 1/sqrt(volume). (since psi^2 ~ probability density from quantum mechanics).  

 I am confused about this. Do i have to multiply it with volume or is psi assumed to be dimensionless?
 Can someone please correct me where i was wrong? 

Thanks
Ajit