RE: Targeted molecular dynamics domain selection question

From: Vermaas, Joshua (Joshua.Vermaas_at_nrel.gov)
Date: Thu Feb 28 2019 - 18:52:29 CST

Hi Aditya,

>From the NAMD user guide describing how the TMD file is used:

TMDFile [$ <$] File for TMD information [$ >$]
Acceptable Values: Path to PDB file
Description: Biased atoms are those whose occupancy (O) is nonzero in the TMD PDB file. Fitted atoms are those whose altloc field is not ` ' or `0', if present, otherwise all biased atoms are fitted. The file must contain no more atoms than the structure file and those atoms present must have the exact same index as the structure file (i.e., the file may contain a truncated atom selection ``index [$ < N$] '' but not an arbitrary selection). The coordinates for the target structure are also taken from the targeted atoms in this file. Non-targeted atoms are ignored. The beta column of targetted atoms is used to designate non-overlapping constraint domains. Forces will be calculated for atoms within a domain separately from atoms of other domains.

You specified based on the beta column, not the occupancy. Is there a particular reason to use TMD rather than colvars? Colvars lets you do transitions between states with lower non-equilibrium work if you choose appropriate collective variables, while TMD as implemented I think can only use RMSD, which is not always the best collective variable to use.

-Josh

On 2019-02-28 16:26:10-07:00 owner-namd-l_at_ks.uiuc.edu wrote:

Dear All,
I had a syntactical question regarding targeted molecular dynamics simulations performed using NAMD. I`m working on a TMD simulation where I want to bias my protein from state A to state B. The system has 58500 atoms, of which 3314 atoms belong to the protein. I label the beta column of the protein atoms in both the input pdb file (stateA.pdb) and the TMD pdb file (target structure) with 1. The beta for all non-protein atoms are set to 0 in both these pdb files. I only want to apply the harmonic restraints to the protein alone and not any other atom in the system. The output file for this trajectory reads as follows:
"Info: TMD domain 0 has 55159 atoms 55159 fitted 55159 biased
Info: TMD domain 1 has 3341 atoms 3341 fitted 3341 biased
Info: 58500 TMD ATOMS
TCL: Running for 30000000 steps
TMD 0 Domain: 0 58.2916 58.2916
TMD 0 Domain: 1 58.2916 6.8374
"
Since the output reads 58500 TMD atoms, I want to clarify if the TMD is being performed on both the solvent and the protein here? Some of the literature on the semantics is a little unclear.
Regards
Aditya

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