Workflow#

Overview#

The following figure illustrates the strongcoca workflow. Here, classes are shown in blue, input parameters and data in orange, and functionalities invoked via external libraries are indicated in green.

# dot -Tsvg workflow.dot -o workflow.svg digraph g { compound=true; graph [ fontname = "helvetica", fontsize = 12.0, rankdir = "TB", bgcolor = "transparent" ]; edge [ fontname = "helvetica", fontsize = 12.0, penwidth = 1.5 ] node [ fontname = "helvetica", fontsize = 12.0, fontcolor = black, shape = ellipse, color = "#a0c9e5", style = filled]; NWChem [ color="#ffca9c", label="NWChem calculation", href="https://nwchemgit.github.io/", shape=box, target="_blank"]; GPAW [ color="#ffca9c", label="GPAW calculation", href="https://wiki.fysik.dtu.dk/gpaw/", shape=box, target="_blank"]; BulkDielec [ color="#ffca9c", label="Bulk dielectric function", shape=box, target="_blank"]; ResponseFunction1 [ label="Response function", href="../moduleref/response_objects.html#strongcoca.response.read_gpaw_tddft", target="_top" ]; ResponseFunction2 [ label="Response function", href="../moduleref/response_objects.html#strongcoca.response.read_nwchem_casida", target="_top" ]; ResponseFunction3 [ label="Response function", href="../moduleref/response_objects.html#strongcoca.response.MieGansResponse", target="_top" ]; PolarizableUnit1 [ label="Polarizable\nunit", href="../moduleref/polarizable_objects.html#polarizable-unit", target="_top" ]; PolarizableUnit2 [ label="...", color="#cccccc" ]; PolarizableUnit3 [ label="Polarizable\nunit", href="../moduleref/polarizable_objects.html#polarizable-unit", target="_top" ]; PolarizableUnit4 [ label="...", color="#cccccc" ]; PolarizableUnit5 [ label="Polarizable\nunit", href="../moduleref/polarizable_objects.html#polarizable-unit", target="_top" ]; PolarizableUnit6 [ label="...", color="#cccccc" ]; Calculator [ label="Calculator", href="../moduleref/calculators.html", target="_top" ]; Energy [ shape=rectangle, color="#a2daa2", label="Correlation energy", fontcolor=black, href="../moduleref/calculators.html#strongcoca.calculators.PolarizabilityCalculator.get_correlation_energy", target="_top"]; Spectrum [ shape=rectangle, color="#a2daa2", label="Excitation spectrum", fontcolor=black, href="../moduleref/calculators.html#strongcoca.calculators.PolarizabilityCalculator.get_dipole_strength_function", target="_top"]; Polarizability [ shape=rectangle, color="#a2daa2", label="Polarizability", fontcolor=black, href="../moduleref/calculators.html#strongcoca.calculators.PolarizabilityCalculator.get_dynamic_polarizability", target="_top"]; GPAW -> ResponseFunction1; NWChem -> ResponseFunction2; BulkDielec -> ResponseFunction3; ResponseFunction1 -> PolarizableUnit1; ResponseFunction1 -> PolarizableUnit2; ResponseFunction2 -> PolarizableUnit3; ResponseFunction2 -> PolarizableUnit4; ResponseFunction3 -> PolarizableUnit5; ResponseFunction3 -> PolarizableUnit6; /* To control the Coupled System label position, we create a node * that is positioned relative to the ResponseFunction and PolarizableUnit * nodes with invisible edges */ CoupledSystemLabel [ shape=rectangle, label="Coupled System", height=0.0, color="transparent"]; ResponseFunction1 -> CoupledSystemLabel[style=invis]; ResponseFunction2 -> CoupledSystemLabel[style=invis]; ResponseFunction3 -> CoupledSystemLabel[style=invis]; subgraph cluster0 { subgraph cluster0sub { PolarizableUnit1; PolarizableUnit2; PolarizableUnit3; PolarizableUnit4; PolarizableUnit5; PolarizableUnit6; color = "#dce7f5"; style = filled; } CoupledSystemLabel -> PolarizableUnit3[style=invis]; CoupledSystemLabel -> PolarizableUnit2[style=invis]; color = "#dce7f5"; style = filled; shape = ellipse; href="../moduleref/coupled_system.html"; target="_top"; } PolarizableUnit3 -> Calculator [ltail=cluster0]; Calculator -> Energy; Calculator -> Spectrum; Calculator -> Polarizability; }

The typical workflow involves the following steps:

  1. compute the excitation spectrum (or spectra) of the underlying units

  2. create one or several response function objects (response) using one of the available parsers for the previously computed excitation spectra

  3. create two ore more polarizable units (PolarizableUnit) using the response function objects from the previous step

  4. combine the polarizable units a coupled system (CoupledSystem)

  5. calculate the correlation energy or excitation spectrum of the coupled system using an appropriate calculator (calculators)

Key concepts#

Response functions#

The response of a system (i.e, for example, atoms, molecules, nanoparticles or bulk materials) can be formally described via response functions. The latter can be observed in several different forms, e.g., absorption or vibrational spectra or dynamics polarizabilities. The Casida representation usually allows for very efficient calculations but is not always available (e.g., such a conversion is not supported for data from RTTDDFT calculations). The most general representation is in terms of the dynamic polarizability.

Polarizable units#

A polarizable unit is an object that is characterized by a specific response as well as a location and orientation in space. Several polarizable units can use the same underlying response function.

Coupled system#

A coupled system combines several polarizable units.

Calculators#

A calculator allows one to evaluate the correlation energy and spectrum of a coupled system. Several different calculators are available. Which of these calculators is best suited for a coupled system depends on the representations of the response functions that are available for the underlying polarizable units, as indicated above.