Parameter fitting to dft energy of "interface system"

Hi, I am a beginner in Gulp.

I have a system of 64 Au and 1 Co2. I have generated the input file as follows -

fit molecule c6 noflag

cartesian angs
Au 10.2707 7.62404 0.0 0.0
Au 10.2707 9.31827 2.396 0.0
Au 7.33623 7.62404 0.0 0.0
Au 7.33623 9.31827 2.396 0.0
Au 8.80348 5.08269 0.0 0.0
Au 8.80348 6.77692 2.396 0.0
Au 8.80348 8.47115 4.79201 0.0
Au 10.2707 2.54135 0.0 0.0
Au 10.2707 4.23558 2.396 0.0
Au 10.2707 5.92981 4.79201 0.0
Au 10.2707 7.62404 7.18801 0.0
Au 4.40174 7.62404 0.0 0.0
Au 4.40174 9.31827 2.396 0.0
Au 5.86899 5.08269 0.0 0.0
Au 5.86899 6.77692 2.396 0.0
Au 5.86899 8.47115 4.79201 0.0
Au 7.33623 2.54135 0.0 0.0
Au 7.33623 4.23558 2.396 0.0
Au 7.33623 5.92981 4.79201 0.0
Au 7.33623 7.62404 7.18801 0.0
Au 8.80348 0.0 0.0 0.0
Au 8.80348 1.69423 2.396 0.0
Au 8.80348 3.38846 4.79201 0.0
Au 8.80348 5.08269 7.18801 0.0
Au 10.2707 0.847115 4.79201 0.0
Au 10.2707 2.54135 7.18801 0.0
Au 1.46725 7.62404 0.0 0.0
Au 1.46725 9.31827 2.396 0.0
Au 2.93449 5.08269 0.0 0.0
Au 2.93449 6.77692 2.396 0.0
Au 2.93449 8.47115 4.79201 0.0
Au 4.40174 2.54135 0.0 0.0
Au 4.40174 4.23558 2.396 0.0
Au 4.40174 5.92981 4.79201 0.0
Au 4.40174 7.62404 7.18801 0.0
Au 5.86899 0.0 0.0 0.0
Au 5.86899 1.69423 2.396 0.0
Au 5.86899 3.38846 4.79201 0.0
Au 5.86899 5.08269 7.18801 0.0
Au 7.33623 0.847115 4.79201 0.0
Au 7.33623 2.54135 7.18801 0.0
Au 8.80348 0.0 7.18801 0.0
Au 0.0 5.08269 0.0 0.0
Au 0.0 6.77692 2.396 0.0
Au 0.0 8.47115 4.79201 0.0
Au 1.46725 2.54135 0.0 0.0
Au 1.46725 4.23558 2.396 0.0
Au 1.46725 5.92981 4.79201 0.0
Au 1.46725 7.62404 7.18801 0.0
Au 2.93449 0.0 0.0 0.0
Au 2.93449 1.69423 2.396 0.0
Au 2.93449 3.38846 4.79201 0.0
Au 2.93449 5.08269 7.18801 0.0
Au 4.40174 0.847115 4.79201 0.0
Au 4.40174 2.54135 7.18801 0.0
Au 5.86899 0.0 7.18801 0.0
Au 0.0 0.0 0.0 0.0
Au 0.0 1.69423 2.396 0.0
Au 0.0 3.38846 4.79201 0.0
Au 0.0 5.08269 7.18801 0.0
Au 1.46725 0.847115 4.79201 0.0
Au 1.46725 2.54135 7.18801 0.0
Au 2.93449 0.0 7.18801 0.0
Au 0.0 0.0 7.18801 0.0
O 9.983999999999924 6.370800000000031 29.3611 -0.35
O 10.063999999999965 8.566799999999944 28.6158 -0.35
C 10.024000000000001 7.4687999999999874 28.9885 0.7

observable
energy au
-0.773849984277604 2173.0
end

…(10 such struc of various energies)

vary
shift
end

lennard epsilon zero 12 6 inter
Au core Au core 6.290000 2.629 0.0 15.0 0 0

lennard epsilon zero 12 6 intra
Au core C core 20.632763 2.7145 0.0 15.0 1 0

lennard epsilon zero 12 6 intra
Au core O core 1.271403 2.8395 0.0 15.0 0 0

lennard epsilon zero 12 6 inter
C core C core 0.063655 2.800 0.0 15.0 0 0

lennard epsilon zero 12 6 inter
O core O core 0.256990 3.050 0.0 15.0 0 0

lennard epsilon zero 12 6 intra
C core O core 0.127901 2.925 0.0 15.0 0 0

dump every test.grs

However, on trying to optimize say, the Au - C LJ parameters, the initial value and the final value obtained are the same. Clearly, I am doing something wrong. Can you please help me out?

You’ve specified “molecule” as a keyword and that the potentials should only act within a molecule (via “intra”) but Au is not a molecular crystal and so if there are no molecules the potentials won’t act on anything. Rather than just copying the urea example directly, it’s best to check what all the options and keywords mean so that you can understand whether they are relevant to a different type of system.

Thank you. The only reason I put ‘molecule’ as a keyword was because I had co2 in the system, not because of Au. I did go through the keywords. But I am still on look to find the right keywords/format so that the crystal and the molecule are distinguishable in the software. Of course, I will keep trying to understand the same. Thanks once again.

Apologies - from a quick read I saw Co2 (rather than CO2) and assumed you were studying an alloy of cobalt with gold rather than adsorption. The point still stands that you shouldn’t be specifying potentials with the gold as “intra” since gold isn’t part of the CO2 molecule.