Hi, I was running geometry optimizations using PSI4. With the keywords
set basis 6-31g(d,p)
optimize(‘b3lyp’)
After the optimization, I have taken the optimized coordinates and converted it to mol2 files to visualize. Some of the compounds containing amide functional groups, trans conformation of -CO and -NH is the ideal. In my structures, it has optimized to be cis amides. Can you help me to rectify this issue? Is this a methodology issue?
Thank you
For geometry optimizations, the choice of basis set and functional is rarely important. Normally, the initial guess matters more. Geometry optimizers will find you a nearby local minimum, not necessarily the global minimum that is further away. Look at your initial guess geometry. It is closer to the cis or to the trans configuration?
Thank you for the response. I will check it.
Hi, I heard about some other method to optimize like “geometric”. For the keywords i shared above, PSI4 uses “optking” method. May I know is there any difference in these two methods regarding the geometry optimizations and the quality of the output geometry?
Not one that’s going to solve this particular issue.
geomeTRIC will probably be better for large systems.
Thank you for the response.