# Overview

## Installation

Entos software is distributed through the Anaconda package manager and can be installed using conda by following instructions at our Anaconda channel. You can install Anaconda here. Recommended: install with the following command which will create a new environment for Qcore:

conda create -n qcore-env -c entos -c conda-forge qcore 'tbb<2021'
conda activate qcore-env

You may also install Qcore in an existing environment with the following command:

conda install -c entos -c conda-forge qcore


## Entos Qcore is easy to run

The Qcore executable can be run with an input in a named input file

qcore my_input.in

on standard input

qcore < my_input.in

or as a string

qcore -s "print(message = 'Hello world')"


Another important feature for workflow integration is that json output can be requested with command-line option -f json. This produces formatted results (provided they are assigned results -- see below) for simple integration in Python or other workflows.

The input language consists of three things: commands, options and result assignments. Commands look like command(...) and options look like option = value. Results from a command can be assigned using foo := command(...). Commands often contain both subcommands and options. Values assigned to an option are typed. All commands and options are documented. Strings in input are specified by single quotes, but these can be dropped when the string contains only letters, numbers and underscore.

Calculations are triggered by top-level commands, with details specified by options and subcommands. For example, to run a simple DFT energy calculation on a water molecule the input reads:

dft(
structure(molecule = water)
xc = pbe
ao = '6-31G*'
)


In this example input, dft() is a command that performs a DFT single-point energy evaluation. It has one subcommand structure() and two options xc and ao.

• The structure() subcommand specifies the molecular structure. One option is to specify molecule, whose value water is a built-in molecule with a pre-defined geometry. Alternatively, the structure could be provided in an XYZ format file via file = 'water.xyz'.
• The options xc and ao specify the exchange-correlation functional and the atomic orbital (AO) basis set, respectively. In this example, we use the PBE functional and the 6-31G* AO basis for the DFT energy evaluation.

This example provides a basic idea on how Qcore input works. In the following, we will walk you through some other examples to demonstrate the capabilities of Qcore.

Next: Energy evaluations