Expectation values

[s.nasiri]

hi

I wanted to know can CASINO compute other expectation value like density, spin density and ... for molecules?
In the manual there is sth for periodic system?
can anyone help me?

[Mike Towler]

Dear Saeed,

This is actually a good question, not least because the documentation is not clear on which expectation values are computable for which kinds of system. So I've just trawled through and updated the documentation (both the manual and the internal keyword listings) and now it hopefully is clear. I've even fixed a few illegal combinations of options which weren't error-trapped. So with the latest 2.13.83 version you should now be able to type 'casinohelp structure_factor' or whatever and understand from the keyword description just what you can do with it.

Just for reference:

The twelve currently available expectation values are as follows (with the letters in in brackets indicating whether they are implemented for ATOMs, MOLecules, PERiodic systems containing atoms, and HOMogeneous systems such as the HEG):

Density - density (ATOM, PER)
Spin-density - spin_density (ATOM, PER)
Reciprocal-space pair-correlation function - pair_corr (PER, HOM)
Spherical real-space pair-correlation function - pair_corr_sph (ATOM, MOL, HOM)
Structure factor - structure_factor (PER, HOM)
Spherically averaged structure factor - struc_factor_sph (HOM)
One-body density matrix (OBDM) - onep_density_mat (HOM)
Two-body density matrix (TBDM) - twop_density_mat (HOM)
Condensate fraction: unbiased TBDM, goes as TBDM${}-{}$OBDM${}^2$ - cond_fraction (HOM)
Momentum density - mom_den (HOM)
Localization tensor - loc_tensor (PER)
Dipole moment - dipole_moment (MOL)

I think that's correct but if someone spots some error in this table then do tell.

Of course some obvious combinations which are missing (e.g. molecular densities) remain an interesting programming project,
if anyone wants to volunteer!

Best wishes,
Mike

[azu]

Hi,
I have what I suspect is a beginner type of problem when plotting the expectation values. I was trying to get an expval.data file with the radial density by setting a density=T in the input file and running a vmc calculation but I am not getting any. Is it because I have to supply an initial expval.data file? Where can I find an example expval.data file?

Thanks for your help,

[Mike Towler]

Hi Azu,

Sorry for the delay in responding. We've been running the CASINO summer school here in Vallico Sotto.

You don't need to supply an initial expval.data file - it should just appear when you activate one of the expectation value flags in the input file (such as density). Without further information I'm not sure why it doesn't..

Could you let me know what version of the code you're using, and what kind of system you're trying to calculate the density for? Could you also read the out file carefully - does it say anything relevant?

Thanks,
Mike