Error with external electric field

masoud37 · 3 Nov 2025, 08:34

Dear Colleagues,
I hope you're doing well.
I have a question regarding an error I encountered in my calculations using CRYSTAL17 and would appreciate your help.

I attempted to apply an external electric field in the 0-0-1 direction to a bulk structure using the following keywords in my input file:

FIELD
0.00194467
0 0 1

However, I received a syntax error. Please see the attached input input and output files.

Previously, I successfully applied an external electric field to 2D nanostructures using the "FIELDCON" keyword without any issues. However, I encountered this error when working with bulk structures.
I would be grateful for any guidance you can provide.

Best regard,
Masoud

aerba · 3 Nov 2025, 09:22

Hi,

The two options you are using, FIELDCON and FIELD, apply a finite electric field along non-periodic and periodic directions, respectively. Thus, FIELDCON can be used for low-dimensional systems (1D, 2D) only.

When the finite electric field is applied along a periodic direction (FIELD option), a supercell must be built along that direction, which requires additional input parameters with respect to the FIELDCON option. A complete input in your case would look something like:

where 4 is the supercell expansion factor along the periodic direction of the field and 40 is the number of Fourier terms for the triangular potential expansion.

For a detailed description of the use of FIELD and FIELDCON, please refer to this tutorial page.

Note

Please, be aware that a more analytical approach is available in CRYSTAL to compute the optical dielectric tensor of a system - that does not require any supercell to be built - through the coupled-perturbed Kohn-Sham (CPKS) method. The input for this option is simply:

CPKS
END

to be inserted before the END of the geometry input block.

You can find a tutorial page on CPKS here.

We do strongly encourage to use CPKS rather than FIELD unless strictly needed.

masoud37 · wrote on 12 Mar 2025, 10:51

Hi,
Thank you very much for your reply!

Best regards,
Masoud