To give a first brief introduction how to write input files, we give an example which is based on the absolutely necessary parameters only.

The basic building blocks of XML are elements, which can contain character content, attributes or other elements. The character content can be a list of values as in the <basevect> element, or text as in the <title> element. Attributes are pairs of the format key="value".

Every exciting input file has to contain at least the following 2 elements inside the <input> root element:

• <structure>
• <groundstate>

The example code:

<?xml version="1.0" encoding="UTF-8" ?>
<input xsi:noNamespaceSchemaLocation="../../../xml/excitinginput.xsd" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 
<structure speciespath="../../../species"  >
    <crystal scale="3.75" >
        <basevect>1 1 0</basevect>
        <basevect>1 0 1</basevect>
        <basevect>0 1 1</basevect>
    </crystal>
    <species speciesfile="Al.xml">
        <atom coord="0 0 0"/>
    </species>
    </structure>
 
<groundstate
    ngridk="a b c" 
    </groundstate>
 
</input>

The structure element contains all information about the crystal.
The ground state element must at least specify a k-point grid ngridk.