Yambo Community Forum

Dear developer,

I am confused about the cofactor used in the function ip_eps2 in dipolesdb.py in yambopy : https://github.com/yambo-code/yambopy/b ... polesdb.py

In line 381 the cofactor was defined as I am curious about why the volume used here is the Recip. lattice volume.
In the equation used to calculate the epsilon or absorption coefficient, it seems that the volume of the lattice cell (with the unit of m^3 or other cubic length) but not that of recip lattice was used.
For example, equation 10 in [PWSCF s epsilon.x users manual] https://web.mit.edu/espresso_v6.1/amd64 ... ps_man.pdf

I have this question because the values of the imaginary part of epsilon calculated by ip_eps2 in yambopy is much larger than that given by "yambo -o c", although they have the same shape.

However, if I used the Direct lattice volume in the cofactor (i.e., spin_deg*8.*np.pi/(self.lattice.lat_vol)), I got valueS much smaller than those calculated by "yambo -o c".

I found that the values of the imaginary part of epsilon calculated by a cofactor of spin_deg*8.*np.pi/(self.lattice.rlat_vol*self.lattice.lat_vol) matched well with that given by "yambo -o c" in both the sample and values. But this definition of cofactor causes more confusion.

Thank you very much for your kind help!
Zhipeng
Tongji University, Shanghai, China

Dear Zhipeng,

Indeed, for the independent-particles response function, there is an intensity mismatch between the yambopy and yambo results. However, the definition of cofactor used in yambopy - the one that you pointed out - is the same one used in Yambo.

Recently, I have found a bug related to the incorrect accounting of the weight of the k-points in the yambopy k-sum, which I patched: In this way, for 3D systems the IP spectrum from yambopy matches exactly that of yambo (at least in my testing). There is still some factor missing in the case of 2D systems though. In order to download the latest patched version, which is not yet available as a release on pip, I suggest to follow these steps: https://wiki.yambo-code.eu/wiki/index.p ... test_patch

Please, don't hesitate to let me know if this fixes it for you or not. Note also that in case of BSE exciton spectra the results from yambopy should match those of yambo.

Best,
Fulvio

Dear Fulvio
Thank you very much for kind reply.
Best
Zhipeng