| This is part of the colvar module |
Calculate the PCA components ( see [46] and [44] ) for a number of provided eigenvectors and an average structure. Performs optimal alignment at every step and reports the rmsd so you know if you are far or close from the average structure. It takes the average structure and eigenvectors in form of a pdb. Note that beta and occupancy values in the pdb are neglected and all the weights are placed to 1 (differently from the RMSD colvar for example)
- Description of components
By default the value of the calculated quantity can be referenced elsewhere in the input file by using the label of the action. Alternatively this Action can be used to be used to calculate the following quantities by employing the keywords listed below. These quanties can be referenced elsewhere in the input by using this Action's label followed by a dot and the name of the quantity required from the list below.
| Quantity | Description |
| eig | the projections on each eigenvalue are stored on values labeled eig-1, eig-2, ... |
| residual | the distance of the present configuration from the configuration supplied as AVERAGE in terms of MSD after optimal alignment |
- Compulsory keywords
| AVERAGE | a file in pdb format containing the reference structure and the atoms involved in the CV. |
| EIGENVECTORS | a file in pdb format containing the reference structure and the atoms involved in the CV. |
- Options
| NUMERICAL_DERIVATIVES | ( default=off ) calculate the derivatives for these quantities numerically |
| NOPBC | ( default=off ) ignore the periodic boundary conditions when calculating distances |
| SQUARED-ROOT | ( default=off ) This should be setted if you want RMSD instead of MSD
|
- Examples
PCARMSD AVERAGE=file.pdb EIGENVECTORS=eigenvectors.pdb
The input is taken so to be compatible with the output you get from g_covar utility of gromacs (suitably adapted to have a pdb input format).
1.8.10 
