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I'm attempting to optimize n-alkane dimers using MP2/DFT in Gaussian09. However the first one or two frequencies are always negative. Can these modes be ignored or do I need to do a tighter optimization?
I searched a lot, they always said you should do scan between two atoms and then fit with Lennard-Jones Equation, but they don't explain which atom should I select or depend on what should I select the atoms. I am a bit confused.
Normally, pairs of atoms connected by chemical bonds are excluded...
opt
keyword, but this wouldn't be needed in your case. — Tyberius ♦ 7 hours ago