I am parameterizing a force field and would need to obtain non-bonded interaction parameters of atoms (e.g., Lennard-Jones parameters).
My primary idea is to obtain a potential energy curve using the Gaussian 09 software and fit the data on that curve to an equation that has non-bonded interaction parameters of atoms (e.g., Lennard-Jones curve).
What I thought was to put two identical molecules and vary the distance between two atoms of these molecules (e.g., using the scan function on redundant coordinator editor) and, therefore, get the energy curve. What I was trying to do was a simple example to get interaction parameters for the oxygen atoms of two water molecules.
I was taking a test with Gaussian at the theory level B3LYP/6-311G++(d,p). Here is the input file:
%nprocshared=4 # opt=modredundant b3lyp/6-311++g(d,p) geom=connectivity Title Card Required 0 1 O -3.09468841 -0.10392610 0.00000000 H -2.13468841 -0.10392610 0.00000000 H -3.41514300 0.80100974 0.00000000 O 3.39491938 0.10392610 0.00000000 H 4.35491938 0.10392610 0.00000000 H 3.07446479 1.00886193 0.00000000 1 2 1.0 3 1.0 2 3 4 5 1.0 6 1.0 5 6 B 1 4 S 10 0.200000
Something I noticed is that the level of theory used (obviously) influences the calculations results. In addition, the initial distance of the water molecules also influences whether the simulation will fail or not (in this example, it works).
Could you kindly tell me if this approach makes sense? Or should I use another software, another type of calculation? Do you have any suggestions on how I could get an energy curve by varying the distance of two non-bonded atoms in the Gaussian? Examples would be appreciated.
With Gaussian and a similar approach I was able to obtain parameters such as bond stretching, angle deformation and dihedral torsion. However, it would be lacking to obtain the non-bonded interaction parameters of atoms.
Things I should consider:
- Do a rigid scan instead a relaxed scan (like the code presented).
- I need a dispersion-corrected density functional methods.