HESSEMAT

HESSEMAT defines the Hesse matrix in Cartesian coordinates ([math]\displaystyle{ \underline{\mathbf{H}}^\mathbf{x} }[/math] ) for the use in Thermodynamic integration with harmonic reference. For a system containing [math]\displaystyle{ N }[/math] atoms, HESSEMAT has [math]\displaystyle{ (3N+1)(N+1) }[/math] lines. The first line specifies potential energy [math]\displaystyle{ V_{0,\mathbf{x}}(\mathbf{x}_0) }[/math] (in eV) of the relaxed system for which [math]\displaystyle{ \underline{\mathbf{H}}^\mathbf{x} }[/math] is computed. The following [math]\displaystyle{ 3N }[/math] 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.