grad – Gradient Data

While not as important as Hessians for VPT2 calculations, nuclear gradients can be used to estimate the significance of certain terms in the VPT2 expansion prior to calculating the associated Hessians, potentially reducing the associated computational demand [Bar11]. Other calculations envisioned for eventual Open Anharmonic implementation would also make more direct use of gradient data.

In order to enable automated parsing of gradient 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 SuperOpanGrad superclass, which requires that the following members be defined for all of its subclasses:

  • gradient – 1-D np.array of np.float – Gradient data in \(\left(\mathrm{E_h\over B}\right)\) 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 SuperOpanGrad.

Implemented Subclasses