How to determine whether delta_approx=.true. needs to be set?

[sevenel]

Dear all,
When calculating phonon linewidth, how to determine whether delta_approx=.true. needs to be set?
When I repeated the example 'q-e-qe-6.7.0/EPW/examples/diamond/epw/' with or notwith the parameter delta_approx=.true. ,
the linewith of phonon are very difference.
best wishes,
zhenqing

[hlee]

Dear zhenqing:

When delta_approx is set to .true. , the “double-delta function” approximation is used; the phonon frequencies are neglected in calculating the imaginary part of the phonon self-energy.
So it is more accurate to set delta_approx to .false. (this is a default value).

Sincerely,

H. Lee