XDATCAR is a output file after the AIMD simulation using VASP code. This file contains the ionic configuration of the system after a given number of ionic steps. The first line is treated as a comment line. The second line provides a universal scaling factor (lattice constant), which is used to scale all lattice vectors and all atomic coordinates (of this value is negative it is interpreted as the total volume of the cell). On the following three lines the three lattice vectors defining the unit cell of the system are given (first line corresponding to the first lattice vector, second to the second, and third to the third). The sixth line specifies the constituting elements. The seventh line supplies the number of atoms per atomic species (one number for each atomic species).