Running a workflow

A workflow in QMFlows consist of a set of computations and the dependencies between them, explicitly declared by the user in the python script. This dependecies and the relation between them form an graph (specifically an acyclic direct graph) that represent these relations.

QMFlows Builds the aforemention graph in order to realize the workflow evaluation order. For instance the figure below represent a simulation where firstly a molecular geometry optimization is carried out using the ADF package and some user defined Settings for the ADF simulation package. Subsequently, using the optimized molecular geometry from the previous step and another Settings for an orca simulation a job to compute the molecular frequencies is carried out.

A python script corresponding with this graph can be

>>> from plams import Molecule
>>> from qmflows import (adf, orca, run, Settings)

>>> inp = Settings(...)
>>> acetonitrile = Molecule(...)

# ADF optimization
>>> optmized_mol_adf = adf(inp, acetonitrile, job_name='acetonitrile_opt')

# Orca Settings definition
>>> s2 = Settings()
>>> s2.specific.orca.main = "freq"
>>> s2.specific.orca.basis.basis = 'sto_sz'
>>> s2.specific.orca.method.functional = 'lda'
>>> s2.specific.orca.method.method = 'dft'

# Orca Frequencies
>>> job_freq = orca(s2, optmized_mol_adf)

# Extract the frequencies from the Orca job
>>> frequencies = job_freq.frequencies

# Run the graph
>>> result = run(frequencies)
>>> print(result)

Up to the invocation of the run() function none of the computations have been executed, it is the run() function which builds and executes the dependencies. Since QMFlows needs to figure out all the dependecies in the script, the run() function takes as argument last dependency (or inner most dependy), which in this case are the frequencies. The reason behind this, is that from the last dependency it is possible to retrace all the dependecies.

QMFlows uses the noodles library under the hook to takes care of the construction and execution of the dependecy graph.