As values in the ~abinit/doc/input_variables/origin_files/abinit_vars.yml file, you can specify numbers, string, arrays, following the standard specification of YAML :

• Wikipedia YAML page
• The official YAML page

Pay attention to strings, as YAML is used. If a chain of character is recognized directly to be a string by YAML, you don't need ticks (' '). Otherwise, you need to put ticks.

For example, if you want to use a link as a value, use a link shortcut like [[abivarname]], but pay attention, sometimes, you will need '[[abivarname]]'. See the doc about link shortcuts at link_shortcuts.

Several “types” are defined to allow sufficient flexibility in the specifications, as follows.

It is the type that contains the other fields.

• abivarname : the name of the variable. Note that the name for input variables of the executables anaddb, aim and optic is always finished with @anaddb, @aim or @optic.
• characteristics : possibly, a specific characteristics of the input variable. To be chosen among the names in ~abinit/doc/input_variables/origin_files/characteristics.yml .
• commentdefault : possibly, some comment about a default value.
• commentdims : possibly, some comment about the dimension of an array.
• defaultval : must be an integer or real value, possibly specified using the types presented below (e.g. !multiplevalue)
• dimensions : either scalar or a list of dimensions, using YML syntax.
• excludes : possible excluded values
• mnemonics : a longer description of the variable role, in a few words
• requires : the input variable is relevant only if this condition is fulfilled
• text : free text describing the input variable
• topics : a string, specified in topics_and_tribes
• varset : a unique “set of variables” to which the variable belong. To be chosen among the names in ~abinit/doc/input_variables/origin_files/varsets.yml .
• vartype : to be chosen among integer, real or string

If there is no information of a type for a specific variable, its value must be “null”.

This is the equivalent to the X*Y syntax in fortran.

  X*Y

will become

  !multiplevalue
    number : X
    value : Y

If X is null, it means that you want to do *Y (all Y)

  !range
     start: 1
     stop: N

As a default value, it means that the default value is 1,2, … N

This type allows to specify conditions on values:

!valuewithconditions
    defaultval: -[[diemix]]
    '70 < [[iprcel]] and [[iprcel]] < 80': '[[diemix]]'
    '[[iscf]]<10': '[[diemix]]'
    '[[iprcel]]==0': '[[diemix]]'

defaultval is the default value if no condition is fulfilled. As condition, please use strings with the most basic expressions, containing <, < =, >, >=, ==, !=, +, -, *, /, etc to allow for further simple parsing !

As a convention, we use “pythonic” way for expressions, so you can use “or”, “and” and “in” also as [[varname]] in [1,2,5] for example …

This type allows to specify values with units:

 !valuewithunit
        units: eV
        value: 100.0

means “100 eV”.

In the YML file (and via the GUI), there are some constraints between variables that have been introduced.

You can specifiy “requires: CONDITION” and “excludes: CONDITION” in the YML file (or fill the fields requires and excludes in the GUI).

If a varname has “requires: CONDITION”, it means that the variable is only relevant when CONDITION is fulfilled.

If a varname has as “excludes: CONDITION”, it means that the specification of the variable in the input file forbids the CONDITION to be fulfilled.