Ab initio study of the compressibility and electronic properties of a molecular organic crystal C$_8$H$_{10}$O$_2$

The structure and electronic properties of a molecular organic crystal octa-3,5-diyn-2,7-diol (C$_8$H$_{10}$O$_2$) were studied in the pressure range from 0 to 1 GPa on the basis of ab initio calculations in the framework of the density functional theory taking into account the dispersion interaction. The compressibilities of C$_8$H$_{10}$O$_2$ were calculated and a significant negative linear compressibility (-44 TPa$^{-1}$) was established, which is caused by a change in the orientation and linear dimensions of molecular structural units relative to the crystallographic axes. Based on a topological analysis of the electron density, it is shown that hydrogen bonds are partially covalent in nature, and their energies are relatively high. It is shown that the upper valence and lower unoccupied electronic states correspond mainly to the states of carbon atoms. The band gap of C$_8$H$_{10}$O$_2$ is calculated and its decrease with increasing pressure is predicted.