# QWalk documentation

The main components of a QMC (or just quantum!) calculation are:

- The Hamiltonian. This is the contents of the SYSTEM section.
- The Trial Wavefunction. This is the contents of the TRIALFUNC section.
- The Method used to evaluate properties. This is the contents of the METHOD section
- The Observables calculated. These are generally inserted in the METHOD section with the keyword AVERAGE.

The input of QWalk is set up to provide those four components of a calculation in a modular way. To assist with this, there are several important helper components:

- Simple Basis functions to represent 3-dimensional functions in real space.
- One-particle orbitals made up of linear combinations of basis functions.
- Converter programs to translate wave functions from DFT and quantum chemistry codes to QWalk format.

## Input rules

- Whitespace is not important
- You can comment a line with '#'
- Keywords are case-insensitive, but string arguments are case-sensitive
- There are three types of keywords
- flags: no argument. For example, 'TMOVES'.
- floats, integers and strings: a single argument. For example, 'VMC_NCONFIG 20000'
- sections: a collection of keywords denoted by curly braces { }. For example, 'METHOD { VMC NBLOCK 50 NDECORR 3 AVERAGE { SK } }'

- The order of keywords is not important unless a keyword is repeated. For example, multiple METHOD sections in an input file will execute them in order.