HESSEMAT

HESSEMAT defines the Hesse matrix in Cartesian coordinates (${\underline {\mathbf {H} }}^{\mathbf {x} }$ ) 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 ${\underline {\mathbf {H} }}^{\mathbf {x} }$ 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.