[CPMD-list] Hydrogen solution?

[Erik Santiso]

Hi everyone! I think I found what's causing the problem with the hydrogen atom run for HCTH/120. There are actually two problems, both related to the SMALL parameter in the functional routines. In the subroutine LSD_HCTH, the value of the SMALL parameter is quite small (1.d-32), and that's what seemed to be causing the unstability with ODIIS. Making it bigger (say 1.d-10) eliminates the unstability, but it still converges to a wrong energy (about -0.4, same that it gave using PCG minimize before). 

The second problem only happens because the system has just one electron (that's why it was working for me with all the other systems but hydrogen). In this case one of the densities (and its gradient) is always zero. Now, the program assigns the SMALL value to both this density and its gradient and that must be making a spurious contribution to the energy (there is an exchange-correlation contribution from an electron that it's not there). 

The only solution I see to this is to do something like what's done in the functionals.f file, i.e. assign zero to the xc contribution for a density that is small, *but* it would have to be done for each density separately (i.e., don't count a contribution coming from the density of the absent electron). At least for HCTH this can be done easily, I'll be fixing this and see if it works.

Thanks to all who replied!

Erik.

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