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Specfun: offdiagonal elements electronphonon selfenergy http://epwforum.uk/viewtopic.php?f=3&t=711 
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Author:  chrisewolf [ Wed Oct 03, 2018 10:19 am ] 
Post subject:  Specfun: offdiagonal elements electronphonon selfenergy 
Dear all, for the spectral function the selfenergy is taken as diagonal in nn'. Giustino's ElPh paper notes that Quote: [...] we are considering for simplicity nondegenerate electronic states, and making the assumption that the offdiagonal elements of the selfenergy can be neglected. In more general situations the righthand side of Eq. (163) needs to be to diagonalized, or alternatively the offdiagonal terms need to be treated perturbatively. I was browsing through the code and I was wondering if EPW checks for the magnitude of the offdiagonal elements at some point (as I would be interested in see if in some cases these are large or small)? specfun has in the header Quote: !! We take the trace of the spectral function to simulate the photoemission !! intensity. I do not consider the caxis average for the time being. !! The main approximation is constant dipole matrix element and diagonal !! selfenergy. The diagonality can be checked numerically. But I do not see where this is done (I blame my very rusty Fortran)... If someone could point to me how/where this is (or could be) evaluated I would be very grateful! Thank you all in advance for your support! Chris 
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