hess – Hessian Data

Nuclear Hessians are key for VPT2 calculations, as the second-order force constants calculated from them by standard harmonic-oscillator methods provide the third- and fourth-order force constants for a system via finite difference differentiation [Bar11] [Blo12].

Todo

Link to HO writeup once composed

In order to enable automated parsing of Hessian data from various computational software packages, a common interface must be defined by which the automated components of opan can access needed data in a uniform manner. This interface is defined by the abstract SuperOpanHess superclass, which requires that the following members be defined for all of its subclasses:

  • hess – 2-D np.array of np.float – Hessian data in \(\left(\mathrm{E_h\over B^2}\right)\) units
  • geom – 1-D np.array of np.float – Geometry data in \(\mathrm B\) units
  • atom_syms – list of str – Atomic symbols in ALL CAPS

Beyond these required members, the below subpages describe the various imported data that are available in the subclasses of SuperOpanHess.

Implemented Subclasses