Interface numerical_hessian

Numerical Hessian calculation by finite differences - provides Hessian for methods for which analytic calculation is not available. Allows calculation from both energies only and from analytical gradients.

Methods and capabilities

The interface implements a single unnamed method; 'method' keyword not necessary

Input structure

The interface requires following blocks in the input:

Keywords used

Keywords specific for this interface:

Examples

The following examples, along with all other files needed to run them, can be found in the directory cuby4/interfaces/numerical_hessian/examples

#===============================================================================
# Numerical hessian example 1 - vibrational analyis
#===============================================================================

# Harmonic vibrational analysis using SCC-DFTB method which does not yield
# analytical Hessian

# Input consists of two steps, geometry optimization and vibrational analysis
job: multistep
steps: opt, freq # Names of the steps

#-------------------------------------------------------------------------------
# Geometry optimization
calculation_opt: 
  job: optimize
  interface: dftb
  method: scc-dftb
  opt_quality: 0.1
  history_freq: 0 # Do not save optimization history
  
  geometry: S66:01 # Water dimer from S66 database
  charge: 0

#-------------------------------------------------------------------------------
# Vibrational analysis
calculation_freq:
  job: frequencies
  interface: numerical_hessian
  geometry: optimized.xyz # Created in teh first step

  calculation: # Calculation of gradients used to construct Hessian
    interface: dftb
    method: scc-dftb
    charge: 0