Re: Parameter Optimization Advice

From: McGuire, Kelly (mcg05004_at_byui.edu)
Date: Fri Mar 01 2019 - 13:34:22 CST

Thanks Lennart, what is your opinion though on parameters for a ligand that can go from a more gas-like phase (ion channel) to a condensed phase (bulk water outside channel)? The charges are fixed, so if the ligand is optimized for bulk water interaction, such as through FFTK, then those interactions could be wrong with sidechains inside a channel. CGENFF gives decent parameters, but often times large penalties for some of the atom parameters in the molecule.

Kelly L. McGuire

PhD Candidate

Biophysics

Department of Physiology and Developmental Biology

Brigham Young University

LSB 3050

Provo, UT 84602

________________________________
From: Lennart Nilsson <Lennart.Nilsson_at_ki.se>
Sent: Friday, March 1, 2019 12:20 PM
To: namd-l_at_ks.uiuc.edu; McGuire, Kelly
Subject: RE: Parameter Optimization Advice

The basic advice is to use the same procedures as were used in developing the parameters of the force field you want to use.

Lennart Nilsson

Karolinska Institutet

From: owner-namd-l_at_ks.uiuc.edu [mailto:owner-namd-l_at_ks.uiuc.edu] On Behalf Of McGuire, Kelly
Sent: den 1 mars 2019 19:13
To: namd-l_at_ks.uiuc.edu
Subject: namd-l: Parameter Optimization Advice

I have gone through and used the FFTK parameter optimization for new molecules to simulate in NAMD. I have also used Gaussian independently of FFTK to get some parameters. I am trying to get a feel for best parameter optimization practices. Here are the questions I have though:

1) FFTK is mostly used to optimize water-molecule interactions and parameters, correct? But, if the molecule is in a semi-vacuum environment, say an ion channel, that has anywhere from 20-100 water molecules, then the molecule is probably interacting more with the sidechains and a vacuum environment than a bulk water environment. Does the FFTK optimization process do anything for interactions other than water molecules?

2) Partial charges are fixed in MD simulations, so even if I used a program like Gaussian to get good partial charges and then put those in my parameter files, how much can I trust and energy calculation process such as adaptive biasing force free energy profiles? In other words, can my choice of partial charges greatly effect my MD simulations? And, what process do you recommend for optimizing parameters?

3) If QM/MM can be done, is that always the better choice because the interactions will be more accurate for the QM region/region of interest? In the QM region, do partial charges change, or are they still fixed during the simulation?

Kelly L. McGuire

PhD Candidate

Biophysics

Department of Physiology and Developmental Biology

Brigham Young University

LSB 3050

Provo, UT 84602

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