In the EEM method (Mortier et al., J. Am. Chem. Soc. 1986, 108, 4315-4320), there are two extra parameters delta_chi and delta_mu. This is different from the QEq, where the input parameters are chi and mu of the isolated atoms.
I am wondering whether the chi and mu parameters in the format of electronegativity option are the effective atomic electronegativity (chi = chi_0 + delta_chi) and hardness (mu = mu_0 + delta_mu) or come directly from those of isolated atoms, chi_0 and mu_0, respectively. I suppose the former is correct? Thank you.
Dear Tanakorn,
The writing of the electronegativity parameters with delta terms is just a formality to point out that the papers for an atom in a molecule may be different from those for the isolated atom. The input is always just the effective values since there is no need to separate the delta part since it only gets added on again.
Regards,
Thank you for the clarification. Another point is I think it might be more clear to describe the meaning of the mu parameter in the manual or to change the mu to eta for atomic hardness according to Parr and Pearson. I first took the mu parameter as a self-Coulomb potential, but mu is in fact the hardness which equals to the self-Coulomb potential divided by 2.
I agree that there is a bit of mix of symbols etc according to which paper you take as your point of reference. I wouldn’t want to change GULP’s convention at this stage for confusing those that have used the code for a while. Hopefully by comparing the equations (and parameters if necessary) then it’s possible to match up to the definition in a different paper. Essentially everything is a quadratic expansion (usually).
Best regards,
Julian