transition dipole moment

Moderators: jzwanzig, jolafc

transition dipole moment

Postby glabcher » Wed Jun 17, 2015 6:12 pm

Dear all,

I need to calculate transition dipole moments for each k-vector k between valence n and conduction n' bands. I am thinking to use simple integral to find (for example x component of) t.d.m. :

m_x= - e * integral (PSI*_n,k (x) * x * PSI_n',k (x) dx )

where PSI_n,k (x) is a real-space wavefunction:

PSI_n,k (r) = sum_G (C_n,k (G) * exp i(k+G)r )

C_n,k plane-wave coefficients with the corresponding G values I am getting from WFK.

Does anyone know if I am doing this right or I should do it in different way?

Thanks!
glabcher
 
Posts: 4
Joined: Mon May 18, 2015 9:09 pm

Re: transition dipole moment

Postby raul_l » Wed Jun 17, 2015 6:38 pm

This only accounts for the local part, no? With separable pseudopotentials or with PAW I think there are additional terms. It might be easier to let abinit calculate the matrix elements and extract pmat from optic.f90.
Raul Laasner
Duke University, MEMS Department
raul_l
 
Posts: 74
Joined: Sun Jan 08, 2012 8:45 pm

Re: transition dipole moment

Postby glabcher » Wed Jun 17, 2015 9:53 pm

Raul,

Thanks for your reply. Does abinit calculate the matrix elements within the DFT method? I know it does for TDDFT. My goal is to obtain electric and magnetic dipole moments from DFT calculations.

And I have one more question about optic.f90. When I run this code, it asks me to provide the name of the data and output files. What is "the data file" in this case? is it WFK file?

Thanks
glabcher
 
Posts: 4
Joined: Mon May 18, 2015 9:09 pm

Re: transition dipole moment

Postby raul_l » Wed Jun 17, 2015 10:52 pm

From what I understand the matrix elements are determined by the calculation of the ddk perturbations, which means TDDFT. optic requires the first-order changes in the wavefunction as input (smarter people can correct me). The relevant calculation should be done in abinit. I'm using optic only for the extraction of the matrix elements.
Raul Laasner
Duke University, MEMS Department
raul_l
 
Posts: 74
Joined: Sun Jan 08, 2012 8:45 pm

Re: transition dipole moment

Postby mverstra » Sat May 20, 2017 12:22 am

See http://www.abinit.org/doc/helpfiles/for ... optic.html

It's DFPT for the ddk, not TDDFT, which would involve finite frequencies for the perturbing E field.

The matrix elements of the d/dk operator give the commutator of H with x, which are related to p or the optical matrix elements you are looking for (pmat). Note that this is a solid by default, so polarization rather than electric dipole. The magnetic moment (again not a simple dipole unless you have a finite system in a big box) has a spin part which you get out of a ground state run. The orbital part is also used in abinit within the PAW formalism, e.g. for NMR calculations. I am not sure where/if this is output.
Matthieu Verstraete
University of Liege, Belgium
mverstra
 
Posts: 618
Joined: Wed Aug 19, 2009 12:01 pm


Return to Theory

Who is online

Users browsing this forum: No registered users and 1 guest

cron