MOMENTS and KPOINTS

[pierre.an...@gmail.com]

Dear all,

The ability to access dipole moments with KPOINTS is a major addition to CP2K. Still, I'm confused as to where the dipole moment actually is in the output file.

I tried the test file provided with CP2K 2026.1, but I cannot find the dipole moment for each k-point or for the crystal.

Could you please let me know where this information is? I'm particularly interested in the total crystal dipole moment.

Kind regards

Pierre 

[Shridhar Shanbhag]

Thanks for the question. The dipole matrix elements with k-point sampling are available under the section titled "Periodic Dipole Matrix Elements" in the output file as shown below.

 !-----------------------------------------------------------------------------!

                     Periodic Dipole Matrix Elements

 Kpoint:  1 , kx:   -0.375000, ky:   -0.375000, kz:    0.000000
   kp  n  m  Re(dx_nm)  Im(dx_nm)  Re(dy_nm)  Im(dy_nm)  Re(dz_nm)  Im(dz_nm)

Under this section you will find a table that gives the real and imaginary x, y and z components of the Bloch-state dipole matrix elements:

μ_nm(k) = <u_nk | ∇_k | u_mk>

computed for each k-point provided by the user along a line or a grid.

These are transition dipole matrix elements between Bloch states. I am not sure what you are referring to as the total crystal dipole moment. The total dipole moment for a system with charge separation is calculated as the vector sum of all individual molecular or bond dipole moments within the crystal structure: μ=Σ q_i d_i. That quantity is not calculated here.

Hope this helps.

Kind regards,

Shridhar