MULTI-RMSD
 This is part of the colvar module

Calculate the RMSD distance moved by a number of separated domains from their positions in a reference structure.

When you have large proteins the calculation of the root mean squared deviation between all the atoms in a reference structure and the instantaneous configuration becomes prohibitively expensive. You may thus instead want to calculate the RMSD between the atoms in a set of domains of your protein and your reference structure. That is to say:

$d(X,X_r) = \sqrt{ \sum_{i} w_i\vert X_i - X_i' \vert^2 }$

where here the sum is over the domains of the protein, $$X_i$$ represents the positions of the atoms in domain $$i$$ in the instantaneous configuration and $$X_i'$$ is the positions of the atoms in domain $$i$$ in the reference configuration. $$w_i$$ is an optional weight.

The distances for each of the domains in the above sum can be calculated using the DRMSD or RMSD measures or using a combination of these distance. The reference configuration is specified in a pdb file like the one below:

ATOM      2  O   ALA     2      -0.926  -2.447  -0.497  1.00  1.00      DIA  O
ATOM      4  HNT ALA     2       0.533  -0.396   1.184  1.00  1.00      DIA  H
ATOM      6  HT1 ALA     2      -0.216  -2.590   1.371  1.00  1.00      DIA  H
ATOM      7  HT2 ALA     2      -0.309  -1.255   2.315  1.00  1.00      DIA  H
ATOM      8  HT3 ALA     2      -1.480  -1.560   1.212  1.00  1.00      DIA  H
ATOM      9  CAY ALA     2      -0.096   2.144  -0.669  1.00  1.00      DIA  C
ATOM     10  HY1 ALA     2       0.871   2.385  -0.588  1.00  1.00      DIA  H
TER
ATOM     12  HY3 ALA     2      -0.520   2.679  -1.400  1.00  1.00      DIA  H
ATOM     14  OY  ALA     2      -1.139   0.931  -0.973  1.00  1.00      DIA  O
ATOM     16  HN  ALA     2       1.713   1.021  -0.873  1.00  1.00      DIA  H
ATOM     18  HA  ALA     2       0.099  -0.774  -2.218  1.00  1.00      DIA  H
ATOM     19  CB  ALA     2       2.063  -1.223  -1.276  1.00  1.00      DIA  C
ATOM     20  HB1 ALA     2       2.670  -0.716  -2.057  1.00  1.00      DIA  H
ATOM     21  HB2 ALA     2       2.556  -1.051  -0.295  1.00  1.00      DIA  H
ATOM     22  HB3 ALA     2       2.070  -2.314  -1.490  1.00  1.00      DIA  H
END


with the TER keyword being used to separate the various domains in you protein.

Compulsory keywords
 REFERENCE a file in pdb format containing the reference structure and the atoms involved in the CV. TYPE ( default=MULTI-SIMPLE ) the manner in which RMSD alignment is performed. Should be MULTI-OPTIMAL, MULTI-OPTIMAL-FAST, MULTI-SIMPLE or MULTI-DRMSD.
Options
 NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically NOPBC ( default=off ) ignore the periodic boundary conditions when calculating distances SQUARED ( default=off ) This should be setted if you want MSD instead of RMSD
Examples

The following tells plumed to calculate the RMSD distance between the positions of the atoms in the reference file and their instantaneous position. The Kearseley algorithm for each of the domains.

MULTI-RMSD REFERENCE=file.pdb TYPE=MULTI-OPTIMAL


The following tells plumed to calculate the RMSD distance btween the positions of the atoms in the domains of reference the reference structure and their instantaneous positions. Here distances are calculated using the DRMSD measure.

MULTI-RMSD REFERENCE=file.pdb TYPE=MULTI-DRMSD


...