4. The AiiDA python interface

In this section we will use an interactive python environment with all the basic AiiDA classes already loaded. There are two variants of this:

The first is a customized ipython shell where all the AiiDA classes, methods and functions are accessible. Type in the terminal

verdi shell

For everyday AiiDA-based operations, i.e. creating, querying and using AiiDA objects, the verdi shell is probably the best tool. You would usually use two terminals, one for the verdi shell and one to execute bash commands.

The second option is based on jupyter notebooks and is great for tutorial purposes. Double click on the Jupyter Apps icon on the Desktop to start a jupyter notebook server. After a few seconds, the browser will open and display the home app. Click on File Browser and select New -> Python 2 (top right corner). You are now inside a jupyter notebook, made of cells where you can type portions of python code. The code will not be executed until you press Shift+Enter from within a cell. Type in the first cell

and execute it. This will set exactly the same environment as the verdi shell. The notebook will be automatically saved upon any modification and when you think you are done, you can export your notebook in many formats by going to File -> Download as. We suggest you to have a look to the drop-down menus Insert and Cell where you will find the main commands to manage the cells of your notebook. The verdi shell and the jupyter notebook are completely equivalent. Use either according to your personal convenience.

Note: you will still need sometimes to type command-line instructions in bash in the first terminal you opened today. To differentiate these from the commands to be typed in the verdi shell, the latter will be marked in this document by a vertical line on the left, like:

# some verdi shell command

while command-line instructions in bash to be typed on a terminal will be encapsulated between horizontal lines:

# some bash command

Alternatively, to avoid changing terminal, you can execute bash commands within the verdi shell or the notebook adding an exclamation mark before the command itself

!some bash command

4.1. Loading a node

Most AiiDA objects are represented by nodes, identified in the database by its pk number (an integer). You can access a node using the following command in the shell:

node = load_node(<PK>)

Load a node using one of the calculation pks visible in the graph you displayed in the previous section of the tutorial. Then get the energy of the calculation with the command


You can also type


and then press TAB to see all the possible output results of the calculation.