# hessian

Compute a hessian of geometrical second derivatives. This command can appear in the global context.

### Options

convergence

Convergence threshold for the iterative subspace solver, tested on on the infinity norm of the residual vectors.

• The type is real
• The default is 1e-6
• The value must be positive
hessian_file

Specifies name of a file to import/export hessian matrix.

If the file exists, the hessian will be read from this file. If the file does not exist, the hessian will be calculated and saved to the file in armadillo binary format.

• This option is deprecated and will be replaced by more general import/export commands
• Only the size of the loaded matrix is checked (i.e. $$3N \times 3N$$)
• The central gradient is still calculated

This option is deprecated.

• The type is string
• There is no default value.
intensities

Flag for whether to compute the infrared intensities.

• The type is bool
• The default is false
linear_dependency_threshold

Threshold for removing linearly dependent vectors based on the square of singular values of the matrix.

• The type is real
• The default is 1e-10
• The value must be positive
mass_weighted_modes

If true, calculate the frequencies and normal modes by using mass-weighted hessian. If false, use the pure hessian.

• The type is bool
• The default is true
max_iter

Maximum number of iterations for the iterative subspace solver.

• The type is int
• The default is 128
• The value must be positive
max_memory

Specify the maximum amount of physical memory that can be used for the analytic hessian calculation. This must not exceed the physically available memory of the machine. If not specified, the program will try to use as much available memory as possible.

• The type is quantity
• There is no default value.
• The value must be positive
method

Method for computing the hessian. The default method will be analytic evaluation when it is available, and semianalytic otherwise.

• The type is string
• There is no default value.
• The value must be one of:
• analytic - Compute hessian as analytic second derivative of energy.
• semianalytic - Compute hessian as numerical derivative of analytic gradient.
• numerical - Compute hessian as numerical second derivative of energy.
name

Specify the name of a set of results.

This option is deprecated.

• The type is string
• There is no default value.
orthonormal_threshold

Threshold for orthonormalization of the suspace vectors.

• The type is real
• The default is 1e-10
• The value must be positive
print_level

Print level.

• The type is int
• There is no default value.
• The value must be one of:
• -2 - No output
• -1 - Minimum output
• 0 - Output that doesn't scale with system size
• 1 - Output that scales linearly with system size
• 2 - (Debugging) output that scales quadratically with system size
• 3 - (Debugging) output that scales cubically with system size
save_normal_modes

Save vibrational frequencies and normal modes to file in Molden format.

• The type is string
• There is no default value.
step_size

Specify the step size for numerical differentiation.

• The type is quantity
• The default is 1e-2 bohr
• The value must be positive
tighter_scf

Flag for whether to use tighter SCF convergence thresholds than those specified in dft or emft. If true, set orbital_grad_threshold 10 times smaller than specified, and energy_threshold 100 times smaller than specified.

• The type is bool
• The default is false