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From: Siladitya Padhi (siladitya.padhi_at_research.iiit.ac.in)
Date: Sun May 14 2017 - 15:55:41 CDT

Dear All,

I am employing the FFTK module to parameterise a molecule that includes a homocyclic ring and a heterocyclic ring, and is 21 atoms big. The quantum mechanical calculations for characterising water interaction sites run fine. However, when I read in the log files from these calculations on FFTK and try to optimise the charges, the optimisation keeps on running without any hint of convergence (I let it run for 14-15 hours, and then eventually terminate it, because I believe the optimisation should take much less time than that).

Here are the initial charges and upper/lower bounds that I am using.
Carbons: initial charge of 0.0, lower bound of -0.5, upper bound of +0.5
Nitrogens: initial charge of 0.0, lower bound of -1.0, upper bound of 0.0
Hydrogens: initial charge of +0.09, lower bound of +0.09, upper bound of +0.09 (all hydrogens being non-polar)

I tried changing the tolerance from 0.005 to 0.01, but that didn't help. I also tried omitting the hydrogens from the optimisation, but that resulted in the error "domain error: argument not in valid range". Could anyone suggest modifications that would lead to proper completion of the optimisation?

Many thanks indeed in advance.

Best regards,
Siladitya Padhi