Two questions about the COMB potential

Hi Jun,

1). Cu cutoffs for Cu-Si alloy is 3.25(R) and 0.10(D), using the mixing
rule gives ~3.07(R) and 0.10(D), which were then set to 3.05 and 0.15.
Mixing rule is a guide for choosing cutoffs, not a definite rule.

2). Cu-Si parameters were obtained by combining parameters for Cu/Cu2O,
Si/SiO2 and Cu/SiO2, which means Cu-Si parameters were not explicit
trained for Cu-Si alloys. They can be further fine-tuned for Cu-Si alloys.
Yes, for well-trained Cu-Si parameters, "Si Cu Cu" and "Si Cu Si"
should/may have different m, c, d, h, n, and beta parameters.

Thanks,
Ray

Dear Dr. Shan:
Thanks very much for your reply and clear explanations. I have another question to consult you. This is related to the “fix qeq/comb” command:
fix ID group-ID qeq/comb Nevery precision keyword value
In the LAMMPS document, the keyword “precision” is explained as this: “the precision argument controls the tolerance for the difference in electronegativity for all atoms during charge equilibration”. I am a little confused about the meaning. For example, if the precision is defined as 0.01, does it mean that the difference between the maximum value and the minimum value of the electronegativity for all atoms should be controled to less than 0.01?

Best,
Jun