Debugging odd transition states in OPTIM
Sometimes in OPTIM high energy transition states will be encountered. There are several strategies for understand why these are occurring.
1. OPTIM and PATHSAMPLE may be able to fine lower energy connections if the calculations are allowed to continue. This can very inefficient. One way of preventing high energy transition states from occurring is to explicitly prevent transition states of a certain energy or above from being allowed. This is done by using the keyword MAXTSENERGY in both PATHSAMPLE and OPTIM.
2. If letting the calculation resolve the problem or MAXTSENERGY does not work looking at the interpolation is necessary. In order to do so, new OPTIM keywords, DEBUG, DUMPNEBEOS, and DUMPNEBXYZ need to be added to print the NEB interpolated energy and coordinates in the files neb.xyz.31267.<n>, and neb.EofS.<n>.31267, where <n> is the number of NEB interpolations.
DEBUG DUMPNEBEOS 300 DUMPNEBXYZ 300
3. For the AMH, for highly anharmonic paths setting very small steps, and visualising the output has been helpful with the use of a combination of the keywords below.
USEDIAG 2 MAXBFGS 0.1 PUSHOFF 0.01 PATH 1000 0.00000000001 BFGSTS 1000 1 10 0.005 100 MAXSTEP 0.05 MAXMAX 0.1 MINMAX 1.0D-4 TRAD 0.1 CONVERGE 0.1 2.0D-6
4. Another set of parameters to explore are the below a larger number of NEWNEB images and cycles can help resolve an interpolation that may have intervening minima between the end points.
NEWNEB 500 10000 0.001 DEBUG DUMPNEBEOS 1 DUMPNEBXYZ 1 BFGSTS 2500 2 30 0.0002
5. PATHSAMPLE can be used to create OPTIM jobs for each NEB candidate instead of chosend based on distance. To do so odata.connect must have:
DIJKSTRA INDEX
And pathdata must have:
DIJINITCONT INDEX
6. Another strategy is to use BHINTERP to use basin-hopping to generate more physically reasonable interpolations between the end points. To do so you to use the keywords BHINTERP and BHDEBUG in OPTIM.
BHDEBUG BHINTERP 5.0 -350.0 100 0.001 1.0 0.4 0.5 0.05 0.8
--mp466 13:48, 23 June 2009 (BST)