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

Code: Select all

```
cofactor = spin_deg*8.*np.pi/(self.lattice.rlat_vol)
```

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