Hi Vladimir, Fan,

Regarding the use of geminals, please have a look at Pascal Bugnion's thesis, which I've placed at

https://www.tcm.phy.cam.ac.uk/~pl275/download/pob_thesis.pdf. Besides describing the CASINO implementation, he looks at the use of geminals for the homogeneous electron gas (see chapters 5 and 6). There are interesting conclusions here; in particular, the single-geminal wave function provides a rather small improvement to the DMC energy over using HF nodes, especially at larger system sizes, but a multi-geminal wave function based on a CI-doubles expansion is much better in this regard (but note that the number of terms in it grows quickly with system size).

I should point out that for the 14-electron gas considered in the thesis one can get better VMC and DMC energies with a truncated CI containing less than 400 determinants (~ 10 optimizable coefficients) than with the multigeminals. This is why I said earlier that I would expect a truncated CI to be a better option than MAGP - but of course each system is a separate story..

How could I update the number of "orbitals allowed" in the input file?

Ok, this is a bug. The MAGP wave function in CASINO has only been used with electron gas orbitals, and for Gaussian orbitals the basis is mistakenly trimmed to the number of electrons (as one would do for a single-Slater-determinant wave function). I'll submit a patch for this shortly.

If I do not specify the g_*,* coefficient, its value will be set to 0 and optimization type to fixed, right? (This would be a useful option since fully spin-unrestricted geminals can always be reduced to diagonal form and upon optimization I don`t wont to break this)

There are indeed keywords in the CASL block to control this:

- Code: Select all
`GEMINAL:`

Default g optimizability : fixed

Default c optimizability : optimizable

Geminal 1:

...

Hey there! I am using CASINO.