This code can help you calculate linear thermal expansion coefficients (LTECs) by Gruneisen theory, based on first-principles calculations. It needs phonon spectra for only several volumes, and can applied to 2D/3D, anisotropic/isotropic materials. Note the calculation is based on the results of VASP and Phonopy. It is based on Python 2.7. (1) Apply strains on your material, optimize the atoms' positions. (2) Calculate phonon spectra in the Brillouin zone with phonopy. Note the Gamma point should be avoided. The mesh.yaml file will be used for subsequent calculations. (3) Calculate the elastic constants of equilibrium volume. (4) Edite the input parameters in grun_tec.in file. (5) Run the code by typing: python grun_tec.py. (6) The results are in LTEC.dat file. There is an example for graphite. You can copy grun_tec.py into directory of example, and type 'python grun_tec.py', then you will see the data of LTECs in the file of LTEC.dat Hopefully you can cite the following papers, if you find this code useful. Many thanks! (^.^) Gang Liu, Jian Zhou and Hui Wang, Phys.Chem.Chem.Phys., 2017, 19, 15187 Gang Liu and Jian Zhou, J. Phys.: Condens. Matter, 2019, 31, 065302