RMC_POT cfg File Format

This document explains the Version 3 RMC_POT cfg configuration format using a concrete example.

Example: Excerpt from aaa.cfg

The following is an excerpt from a typical cfg file. The first line must be preserved verbatim.

aaa.cfg

 (Version 3 format configuration file) !file created by SimpleCfg::save !
comment sio2


               0               0               0               0               0               0               0               0               0               0               0               0               0 moves gen, tried, acc, pot-acc, swap-gen, swap-acc, E0shift-gen, E0shift-acc, I(Q)mu-gen, I(Q)mu-acc, f'shift-gen, f'shift-acc, goodnonlinreg
          0              configurations saved
 
        300 molecules of all types
          3 types of molecules 
          1 is the largest number of atoms in a molecule 
          0 Euler angles are provided 
 
          F (box is cubic)	
            Defining vectors are: 
              7.635000   0.000000   0.000000
              0.000000   7.635000   0.000000
              0.000000   0.000000   7.635000

        100 molecules of type  1
          1 atomic sites 
              0.000000   0.000000   0.000000
 
        160 molecules of type  2
          1 atomic sites 
              0.000000   0.000000   0.000000
 
         40 molecules of type  3
          1 atomic sites 
              0.000000   0.000000   0.000000
 
 0.469499871368697  0.860252930085134  0.143086911460380
 0.506517212128356  0.782365058978389  -0.044207465828422
 0.424472315756385  -0.948087206561890  0.159658069155206
 0.519361825199738  0.779885605592665  0.290516312927309
 0.447290765121153  -0.667661128775380  0.036773942632613
 0.454085926915521  0.047929672102161  -0.361803986548788
 0.382807239777341  -0.107567570857891  -0.467392567413229
 0.322093601270465  0.152408219423707  -0.261319106024885
 0.617544006208252  0.075438279462999  -0.325725383837590
 0.032760774708579  0.186415932416503  -0.177798618166339
 0.899782755769483  0.086198503510151  0.756794255625409

Explanation of Each Section (in File Order)

  1. First line (required)

    The first line is:

     (Version 3 format configuration file) !file created by SimpleCfg::save !

    Copy this line exactly as shown; do not modify it.

  2. Comment line

    comment sio2

    This is a comment.

  3. Total count and molecular summary (when using molecular information)

    The molecular information begins at line 8 of the example.

    300 molecules of all types

    In this example, RMC is performed using atomic information only, without explicit molecular information. Accordingly, this field gives the total number of atoms.

  4. Number of types, molecule size, and Euler angles

    3 types of molecules 
1 is the largest number of atoms in a molecule 
0 Euler angles are provided

    Specify the number of atomic species. Here there are three species, so the value is 3. Because molecular information is not used, set the second line to 1 and the third to 0.

  5. Simulation cell (box) information

      F (box is cubic)	
    Defining vectors are: 
      7.635000   0.000000   0.000000
      0.000000   7.635000   0.000000
      0.000000   0.000000   7.635000

    For the cubic cell used here, enter half the edge length, L/2. In this example, 15.27 Å / 2 = 7.635 Å.

  6. Population and number of sites for each atomic (molecular) type

    Next, specify the number of atoms of each species.

    100 molecules of type  1
  1 atomic sites 
      0.000000   0.000000   0.000000

160 molecules of type  2
  1 atomic sites 
      0.000000   0.000000   0.000000

 40 molecules of type  3
  1 atomic sites 
      0.000000   0.000000   0.000000

    In this example, type 1 has 100 atoms, type 2 has 160 atoms, and type 3 has 40 atoms. The atomic coordinates that follow are ordered by species: type 1, then type 2, then type 3.

  7. Coordinate block (end of file)

    Atomic coordinates appear at the end of the file.

     0.469499871368697  0.860252930085134  0.143086911460380
 0.506517212128356  0.782365058978389  -0.044207465828422
 0.424472315756385  -0.948087206561890  0.159658069155206
 0.519361825199738  0.779885605592665  0.290516312927309
 0.447290765121153  -0.667661128775380  0.036773942632613
 0.454085926915521  0.047929672102161  -0.361803986548788
 0.382807239777341  -0.107567570857891  -0.467392567413229
 0.322093601270465  0.152408219423707  -0.261319106024885
 0.617544006208252  0.075438279462999  -0.325725383837590
 0.032760774708579  0.186415932416503  -0.177798618166339
 0.899782755769483  0.086198503510151  0.756794255625409

    These coordinates are expressed in the range (-1, 1), with the center of the cubic cell as the origin. In other words, atomic coordinates are scaled relative to the cell size. For example, if the edge length is L = 15.27 Å, a cfg coordinate of (0.5, 0.5, 0.5) corresponds to the Cartesian position (3.8175 Å, 3.8175 Å, 3.8175 Å) relative to the cell center.

    \[\begin{split}x_{\mathrm{center}} = x_{\mathrm{cfg}}\frac{L}{2}\\ x_{\mathrm{corner}} = (x_{\mathrm{center}}+L/2)\bmod L\\ x_{\mathrm{cfg}} = 2\frac{x_{\mathrm{center}}}{L}\end{split}\]

    The conversion is given by these equations. Here, \(x_{\mathrm{center}}\) is the Cartesian coordinate relative to the cell center, while \(x_{\mathrm{corner}}\) uses the cell corner as its origin. When converting to VASP Cartesian coordinates, check the lattice vectors and origin convention used in the POSCAR file.

Practical Notes / Checklist

  • Do not delete or modify the first (version) line.

  • Ensure that the counts and ordering of types, atomic sites, and molecules of type conform to the requirements of the software reading the cfg file.

  • List all coordinates of type 1 first, followed by all coordinates of type 2, and so on (as expected by many implementations).

  • In this example, the defining vectors represent the half-edge length \(L/2\) of the cubic cell. Verify the coordinate conventions before applying this interpretation to other file formats.