I am trying to optimize a pair of planar molecules interacting with each other (in a plane) by 2 Hydrogen bonds ( 2 O-H...O hydrogen bonds) using MOPAC2012 package on Linux. During PM7 optimization, these 2 molecules are losing planarity and making a V-shape geometry. When I used PM6-DH2 method, the formation of V-shaped geometry is reduced.
Please can any one suggest that how to tackle this problem.
Options used for mopac run :
PM7 PRECISE EF T=48H THREADS=4 DUMP=600 GRAPHF
Perhaps you could provide specific information on the molecules in the calculation? Without additional information it is challenging to determine the underlying issue.
One possible cause is a poor starting geometry with inadequate time to reach a stable geometry (or the calculation reaches a very flat point on the potential energy surface and is identified as a local minimum which is higher in energy than the global minimum). Also. an invalid charge state.
Please send me the corresponding structure, then I can check and suggest a solution for this issue.
Dear All,
Thanks for your suggestions and sorry for late reply.
Dear Mathew: after your suggestion , I have tried with stacked molecules with different configurations. What I observed is that molecules are stacked an tilted over each other. But planarity is not maintained yet. I think I have to try little bit more.
Dear Haresh: there are 61 atoms in one molecule.
Dear Davood: Thanks for you reply. But being collaborative work, I can't share structure with you now.
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