I am doing geometrical optimisation of an organic molecule on a surface. During this i encountered a message **** Too many failed attempts to optimise **** and my gulp job shut down. What is the cause of this error and how can i avoid it ?
Hard to say exactly from just the message alone what the issue is. However, failed optimisations usually mean there is an issue with the force field you are using. In particular, if your potentials aren’t smooth (i.e. if you have discontinuities due to cutoffs) then any optimiser will fail since the energy landscape isn’t continuous. So I’d check your potentials and use tapers to smooth any cutoffs where possible.
Thanks for the prompt reply. One More question how this potential taper can be applied? I checked the manual and found a option “qtaper”. Can this option be applied to get smooth potential?
By the way I am using ReaxFF force field.
Tapers are applied to 2 body potentials via cutp. However, if you are using ReaxFF then things are generally already tapered in the GULP implementation. Since ReaxFF doesn’t have analytic 2nd derivatives at present this makes optimisation harder.
Any solutions to this? I am attaching my input file in the link below.
Having looked at your input file it seems you limited the number of optimisation cycles to only 50 which is why the calculation stopped. When using conjugate gradients convergence will be slow - the number of steps required is comparable to the number of variables you have which is 2940 & so it’s not surprising that the run didn’t converge. If you set the number of optimisation steps to 3000 (or keep restarting) then hopefully it will converge as planned.