Difference in lambda and l_a2f

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Joined: Fri Nov 19, 2021 3:15 pm
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Difference in lambda and l_a2f

Post by dangicdj »

Dear Ms/Mr,

I started recently using EPW to calculate superconductors' transition temperatures. I am puzzled by the following result I am getting:
lambda : 1.7232748
lambda_tr : 2.3592576

Estimated Allen-Dynes Tc

logavg = 0.0119050 l_a2f = 1.1669279
I am guessing the first lambda is just the average of phonon modes lambdas over the Brillouin zone. Also, I assume that l_a2f is calculated using Eq. (1) and (3) from https://journals.aps.org/prb/pdf/10.110 ... evB.12.905 . I would expect these two values to be equal and looking through previous posts here they appear to be the same in most posts.

My question is should they always be equal? If so, does them being different tell me about what I need to change in my approach (smearing parameters, grids, etc). If they should not always be equal, is there a way to get l_a2f though mode resolved lambdas? Also, I would like to add that just looking at the formulas I would expect them to be equal always.

Kind regards,


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