Yambo Community Forum

Posted: **Tue Aug 12, 2025 10:13 am**

Dear Yambo Developers,

After the diagonalisation in BSE, in the eps output file, I get the diamagnetic terms printed:

# Diamagnetic term                                
# Ao                                              :  -247.905334    [nel]
# A                                               :  -247.917587    [nel]

Can I know how these terms are calculated and what is the units. Is it Bohr^2? The equation used to calculate in the code might help.

Regards,
Jagjit

Posted: **Fri Sep 12, 2025 9:05 am**

Dear Jagjit,
the Diamagnetic term is computed according to Eqs. (23a) and (48a) in PRB 95, 155203 (2017). See also Eq.(1.12) in PRB 48, 11705 (1993) with n=e=1 since the code uses atomic units.
Accordingly, the value is in number of electrons in the unit cell.

As discussed in both PRBs, the result suffers of convergence issues w.r.t. the number of bands used in the calculation, and conductivity sum rule breaking. For how the diamagnetic term is related to the Drude term (see discussion around eq. (34) in the first PRB).

Best,
D.

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