# RMC_POT cfg File Format This document explains the Version 3 RMC_POT `cfg` configuration format using a concrete example. ![](figs/aaa.vasp.png) --- ## Example: Excerpt from `aaa.cfg` The following is an excerpt from a typical `cfg` file. The first line must be preserved verbatim. aaa.cfg ```text (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: ```{code} (Version 3 format configuration file) !file created by SimpleCfg::save ! ``` Copy this line exactly as shown; do not modify it. 2. Comment line ```{code} 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. ```{code} 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 ```{code} 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 ```{code} 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. ```{code} 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. ```{code} 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. ```{math} 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} ``` 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. ---