  MNDO-based semiempirical methods in quantum chemistry have found widespread
application in the modelling of large and complex systems. A method for the
analytic evaluation of first and second derivatives of molecular properties
against semiempirical parameters in MNDO-based NDDO-descendant models is
presented, and the resultant parameter Hessian is compared against the
approximant currently used in parameterization for the PMx models. As a proof
of concept, the exact parameter Hessian is employed in a limited
reparameterization of MNDO for the elements C, H, N, O and F using 1206
molecules for reference data.
