Install xcrysden-data by entering the following commands in the terminal:
sudo apt update sudo apt install xcrysden-data
Description:
Crystalline and Molecular Structure Visualizer (Data Files)
XCrySDen is a crystalline and molecular structure visualisation program, which aims at display of isosurfaces and contours, which can be superimposed on crystalline structures and interactively rotated and manipulated. It can run on most UNIX platforms, without any special hardware requirements. . This package contains the architecture independent files.
Homepage: http://www.xcrysden.org/
Version: 1.5.60-1build3
Section: universe/science