Inputs to qdsim

parse_unit(input_dict)

Parses the [units] section of the system TOML file. It takes two variables:

Parameters obtained:

• energy_unit_name [Default: ha]: Specifies the energy units. Typically eV, meV, cm^-1, or ha.
• time_unit_name [Default: au]: Specifies the time units. Typically fs, or au.

parse_system(sys_inp, unit)

Parses the [system] portion of the system file for the Hamiltonian and converts it to atomic units for internal use.

Parameters obtained:

• type [Default: real, Optionally: complex]: the type of elements in the Hamiltonian.
• Htype [Default: file]: How to parse the Hamiltonian file. Typically file to read a file, nearest_neighbor to specify the Hamiltonian as a nearest-neighbor tight-binding model, or nearest_neighbor_cavity for a Hamiltonian consisting of a nearest-neighbor tight-binding part and a cavity with interacts with all the sites.

Then the Hamiltonian needs to be specified in the energy units that are being used. This can be done in several ways depending on the value of Htype:

• if Htype = file, put in the variable, Hamiltonian with the name of a file containing the elements of the Hamiltonian matrix.
• if Htype = "nearest_neighbor", specify the following variables:
  • site_energy: the energy of each site
  • coupling: the intersite coupling element
  • num_sites: the number of sites
• if Htype = "nearest_neighbor_cavity", in addition to the same variables as the Htype = "nearest_neighbor" case, also specify:
  • cavity_energy: the energy of the cavity mode
  • cavity_coupling: coupling of the cavity to the monomers

The parameter is_QuAPI [Default: true] specifies if the specified system Hamiltonian should be interpreted to be a part of the QuAPI system-bath Hamiltonian form or not.

If external time-dependent fields have to be incorporated, the subsection [external_field] should be used. By default no external fields are involved. If used, the subsection would have two variables:

• coupling_op: the operator through which the external time-dependent field interacts with the system
• V_t: this is a single line expression which evaluates to the value of the field as a function of time, t. This variable needs to be called t.

parse_bath(baths, sys, unit)

This function parses the bath(s) interacting with the system. Currently only harmonic baths are supported.

Parameters:

• The temperature for the simulation needs to be specfied. This can be done in one of two ways:
  • beta in units of 1/ha for the inverse temperature $\beta = \frac{1}{k_BT}$.
  • or temperature in the units of Kelvin.
• A list of baths that interact with the system specified under [[baths.bath]] heading in the TOML file. Each bath is parsed by QuantumDynamicsCLI.ParseInput.get_bath.

get_bath(b, unit)

Parse individual baths

Parameters:

• type [Default: ohmic]: Type of harmonic bath. Can be ohmic, drude_lorentz, tabular, tabular_jw_over_w, huang_rhys
• num_osc: Number of oscillators to discretise the bath to

The parameters for the bath are specified in different ways for each different bath:

• if type="ohmic", the bath spectral density $J(\omega)=\frac{2\pi}{\Delta s^2}\hbar\xi\omega_c\exp\left(-\frac{\omega}{\omega_c}\right)$
  • xi: dimensionless Kondo parameter ($\xi$)
  • omegac: cutoff frequency ($\omega_c$) in energy units
  • Ds [Default: 2]: $\Delta s$ value. Typically set to 1 for exciton transfer problems.
  • npoints [Default: 100000]: Number of points used in integration for the influence functional coefficients.
  • omega_max [Default: 30.0 * omegac]: Upper limit of influence functional coefficient integrations
• if type="drude_lorentz", the bath spectral density $J(\omega) = \frac{2\lambda}{\Delta s^2}\frac{\omega \gamma}{\omega^2+\gamma^2}$
  • lambda: reorganization energy, $\lambda$, in energy units
  • gamma: cutoff frequency, $\gamma$, in energy units
  • Ds [Default: 2]: $\Delta s$ value. Typically set to 1 for exciton transfer problems.
  • npoints [Default: 100000]: Number of points used in integration for the influence functional coefficients.
  • omega_max [Default: 1000.0 * gamma]: Upper limit of influence functional coefficient integrations
• if type="tabular", the bath spectral density is provided as a table in the file specified in jw_file
• if type="huang_rhys", the bath spectral density is provided in the form of a table of frequency-dependent Huang-Rhys factors in the file specified in huang_rhys_file

parse_operator(op, Hamiltonian; mat_type::String="real")

Return the matrix form of the operator op for the system with given Hamiltonian.

The following forms of op are recognised:

• P_n: population of the nth state/the diagonal operator |n⟩⟨n|
• F_n: rate of change of population of the nthe state
• O_n,m: the off-diagonal operator |n⟩⟨m|
• id: the identity operator
• anything else is interpretted as a file which contains the matrix form of the operator

For the last item, mat_type can be the string "complex" which implies that the matrix is complex.