Interface numerical_gradient

Numerical gradient calculation by finite differences - provides gradient for methods for which analytic gradient is not available.

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_gradient/examples

#===============================================================================
# Numerical gradient example 1 - optimization with numerical gradient
#===============================================================================

# Optimize water molecule
job: optimize
opt_quality: 0.1
geometry: A24:water

# Use numerical gradient
interface: numerical_gradient

# This block is used to evaluate energy of each point needed for the
# construction of the gradient:
calculation:
  interface: mopac
  method: AM1
  charge: 0

#===============================================================================
# Numerical gradient example 2 - comparison of analytical and numerical gradient
#===============================================================================

# Prints the difference between numerical and analytical gradient.

# Calculate and print gradient
job: gradient

# Water molecule from A24 database
geometry: A24:water

# Here, advanced YAML syntax is used to define the calculation setup once
# and use it at multiple places later
shared_calc: &calc
  interface: mopac
  method: pm6
  charge: 0

# The Mixer interface is used to calculate the differnce
interface: mixer
mixer_weight_a: 1.0
mixer_weight_b: -1.0

# Numerical gradient calculation
calculation_a:
  interface: numerical_gradient
  calculation:
    <<: *calc # This loads the named block defined above

# Analytical gradient directly from Mopac
calculation_b:
  <<: *calc # This loads the named block defined above
  mopac_precise: yes # Ask mopac to yield more accurate gradient