How to know the specific content of the dielectric matrix

[shan dong]

Dear all,
When we do a linear response calculation(IP,RPA,BSE),we can get the o-eps file. But how to know the specific content of the dielectric matrix or the the dimensions of the dielectric matrix,such as 3*3 ?
Waiting for your reply.

[Daniele Varsano]

Dear Shan Dong,
the microscopic dielectric matrix is calculated in reciprocal space and the dimensions are Ng x Ng' and it is stored in the ndb.em1s database. If I well understood your question you are interested in the macroscopic part (G=G'=0) in the limit q=0.
What you have in the o.eps file is the diagonal part along the direction you choose in input given by the direction of the dielectric field: (BLongDir for BSE, LongDrXd for RPA), so you can access eps_xx, eps_yy, eps_zz by performing three calculations along (100), (010) and (001) directions.
If you are interested in the off-diagonal components you may have a look to this thread.

Best,
Daniele