Saikat, Your issue here is that you are using the default value of:
MD.MaxForceTol 0.04 eV/Ang because you are not using it in your fdf file. For what you are trying to accomplish, I think a MD.MaxForceTol of about 0.001 eV/Ang is more appropriate.This is a good target for small molecules. Try using far fewer MD.NumCGsteps too, I usually use about 30-50 at a time so that if something goes wrong you can trace it without waiting forever, a good practice if you're moving from small molecules to molecules adsorbed onto a surface or something. MaxSCFiterations is very high as well, should something unfortunate happen with your convergence. It won't affect anything here, though. You can also use: UseSaveData .true. To restart simulations that go to the full # of CG steps using saved density matrices and atomic positions, and recent CG history. The reason why you were seeing negative frequencies is because your geometry optimization is not finding the global minimum, so that when atoms are displaced in the FC step by very small amounts, it might find a lower energy state. This topic is discussed at length elsewhere on the list. -- Abraham Hmiel Katherine Belz Groves Fellow in Nanoscience Xue Group, College of Nanoscale Science and Engineering at SUNY Albany
