HESSEMAT

HESSEMAT defines the Hesse matrix in Cartesian coordinates (${\underset{\_}{\mathbf{𝐇}}}^{\mathbf{𝐱}}$ ) for the use in Thermodynamic integration with harmonic reference. For a system containing $N$ atoms, HESSEMAT has $(3N+1)(N+1)$ lines. The first line specifies potential energy $V_{0,\mathbf{𝐱}}({\mathbf{𝐱}}_0)$ (in eV) of the relaxed system for which ${\underset{\_}{\mathbf{𝐇}}}^{\mathbf{𝐱}}$ is computed. The following $3N$ lines are reserved for positions in fractional coordinates of all atoms constituting the system, whereby each line should contain three components of position vector of a single atom. The remaining part of HESSEMAT consist of $3N$ block of $N+1$ lines each. Each block contains information related to a single eigenmode of ${\underset{\_}{\mathbf{𝐇}}}^{\mathbf{𝐱}}$: the first line specified the eigenvalue (in eV/${\AA }^2$) and remaining and $N$ lines the eigenvector (in Cartesian coordinates) in a 3-column format.