Retrieving results

In this section, we describe how to get the results of a calculation after it has been parsed by AiiDA, or the input and output of a generic Node. When a calculation is done on the remote computer, AiiDA will retrieve the results and try to parse the results with the default parser, if one is available for the given calculation. These results are stored in new nodes, and connected as output of the calculation. Of course, it is possible to directly check the output nodes for a given calculation and get their content. However, AiiDA provides a way to directly access the results, using the CalcJobResultManager class, described in the next section.

The CalcJobResultManager

Prerequisites

Before getting the calculation results, we need a correctly finished and parsed CalcJobNode. For example this can be a Quantum ESPRESSO pw.x calculation. You can load such a calculation – we’ll call it calc – with the command

from aiida.orm import load_node
calc = load_node(YOURPK)

either in verdi shell, or in a python script (as described here). YOURPK should be substituted by a valid calculation PK in your database.

Using the CalcJobResultManager instance

Each CalcJobNode has a res attribute that is a CalcJobResultManager instance and gives direct access to parsed data. You can access it as

calc.res

To get all the possible keys that were parsed, you can convert the instance into a list. For instance, if you type

print(list(calc.res))

you will get something like this:

['rho_cutoff', 'energy', 'energy_units', ...]

(the list of keys has been cut for clarity: you will get many more keys).

Once you know which keys have been parsed, you can access the parsed value simply as an attribute of the res CalcJobResultManager. For instance, to get the final total energy, you can use

print(calc.res.energy)

that will print the total energy in units of eV, as also stated in the energy_units key

print(calc.res.energy_units)

Similarly, you can get any other parsed value, for any code that provides a parser.

Hint

The CalcJobResultManager is also integrated with the iPython/verdi shell completion mechanism: if calc is a valid CalcJobNode, you can type

calc.res.

and then press the TAB key of the keyboard to get/complete the list of valid parsed properties for the calculation calc.

Calculations and workflows inputs and outputs

In the following, we will show the methods to access the input and output nodes of a given calculation or workflow.

Again, we start by loading a node from the database. Unlike before, this can be any type of node. For example, if we have a the node with PK 17:

from aiida.orm import load_node
calc = load_node(17)

Now, we want to find the nodes which have a direct input or output link to this node. The node has several methods to extract this information: get_outgoing(), get_incoming().

The most practical way to access this information for a calculation (or workflow), when limiting solely to INPUT_CALC and CREATE (or INPUT_WORK and RETURN, respectively), especially when working on the verdi shell, is by means of the .inputs and .outputs attributes.

The .inputs attribute can be used to list and access the input nodes. The names of the input links can be printed by list(calc.inputs) or interactively by calc.inputs. + TAB. As an example, suppose that calc has an input KpointsData object under the linkname kpoints. The command

calc.inputs.kpoints

returns the KpointsData object.

Similarly the .outputs attribute can be used to display the outputs of calc. Suppose that calc has an output FolderData with linkname retrieved, then the command

calc.outputs.retrieved

returns the FolderData object.