Input¶

General remarks on input structure and parsing¶

• Most keys are optionals. Defaults values will be used for keys that are not specified in the input

• Keys/blocks can either be unique (i.e. they can appear in the input only once) or non-unique. (i.e. they can appear multiple times in the input)

• The order in which keys or blocks are specified in the input does not matter. Possible exceptions to this rule are a) the content of non-standard blocks b) some non-unique keys/blocks)

• Comments in the input file start with one of the following characters: #, !, :::

  # this is a comment
  ! this is also a comment
  :: yet another comment
  

• Empty lines are ignored

• The input parsing is case insensitive (except for string values):

  # this:
  UseSymmetry false
  # is equivalent to this:
  USESYMMETRY FALSE
  

• Indentation does not matter and multiple spaces are treaded as a single space (except for string values):

  # this:
       UseSymmetry     false
  # is equivalent to this:
  UseSymmetry false
  

• Environment variables in the input will be replaced by their value. We only support simple substitution of variables (optionally surrounded by {}). All other parameter expansion features of the POSIX shell (e.g. default values) are not supported. Expansion of a variable can be prevented by prefixing the leading dollar ($) with a backslash (\). Note that variables which are not set will expand to an empty string, just like in a shell:

  File $SOME_DIRECTORY/file.txt
  File ${SOME_DIRECTORY}_BACKUP/file.txt
  Key  \$WILL_NOT_EXPAND
  

Keys¶

Key-value pairs have the following structure:

KeyName Value

Possible types of keys:

bool key

The value is a single Boolean (logical) value. The value can be True (equivalently Yes) or False (equivalently No.). Not specifying any value is equivalent to specifying True. Example:

KeyName Yes

integer key

The value is a single integer number. Example:

KeyName 3

float key

The value is a single float number. For scientific notation, the E-notation is used (e.g. \(-2.5 \times 10^{-3}\) can be expressed as -2.5E-3). The decimal separator should be a dot (.), and not a comma (,). Example:

KeyName -2.5E-3

Note that fractions (of integers) can also be used:

KeyName 1/3    (equivalent to: 0.33333333333...)

string key

The value is a string, which can include white spaces. Only ASCII characters are allowed. Example:

KeyName Lorem ipsum dolor sit amet

multiple_choice key

The value should be a single word among the list options for that key (the options are listed in the documentation of the key). Example:

KeyName SomeOption

integer_list key

The value is list of integer numbers. Example:

KeyName 1 6 0 9 -10

Note that one can also specify ranges of integers by specifying the interval and (optionally) the step size separated by colons:

KeyName 1:5       (equivalent to: 1 2 3 4 5)
KeyName 2:10:2    (equivalent to: 2 4 6 8 10)
KeyName 20:10:-2  (equivalent to: 20 18 16 14 12 10)

Note also that ranges can be freely combined with individual numbers:

KeyName 1:5 10 20  (equivalent to: 1 2 3 4 5 10 20)

float_list key

The value is list of float numbers. The convention for float numbers is the same as for Float keys. Example:

KeyName 0.1 1.0E-2 1.3

Float lists can also be specified as a range with equidistant points, by specifying the interval’s boundaries (inclusive) as well as the number of desired subintervals separated by colons:

KeyName 1.0:1.5:5  (equivalent to: 1.0 1.1 1.2 1.3 1.4 1.5)

Range specifications can be freely combined with each other and single numbers:

KeyName 0.0 1.0:1.5:5 2.0:3.0:10

Blocks¶

Blocks give a hierarchical structure to the input, grouping together related keys (and possibly sub-blocks). In the input, blocks generally span multiple lines, and have the following structure:

BlockName
   KeyName1 value1
   KeyName2 value2
   ...
End

Headers

For some blocks it is possible (or necessary) to specify a header next to the block name:

BlockName someHeader
   KeyName1 value1
   KeyName2 value2
   ...
End

Compact notation

It is possible to specify multiple key-value pairs of a block on a single line using the following notation:

# This:
BlockName KeyName1=value1 KeyName2=value2

# is equivalent to this:
BlockName
   KeyName1 value1
   KeyName2 value2
End

Notes on compact notation:

• The compact notation cannot be used for blocks with headers.

• Spaces (blanks) between the key, the equal sign and the value are ignored. However, if a value itself needs to contain spaces (e.g. because it is a list, or a number followed by a unit), the entire value must be put in either single or double quotes:

  # This is OK:
  BlockName Key1=value Key2 = "5.6 [eV]" Key3='5 7 3 2'
  # ... and equivalent to:
  BlockName
     Key1  value
     Key2  5.6 [eV]
     Key3  5 7 3 2
  End
  
  # This is NOT OK:
  BlockName Key1=value Key2 = 5.6 [eV] Key3=5 7 3 2
  

Non-standard Blocks

A special type of block is the non-standard block. These blocks are used for parts of the input that do not follow the usual key-value paradigm.

A notable example of a non-standard block is the Atoms block (in which the atomic coordinates and atom types are defined).

Including an external file¶

You can include an external ASCII file in the input with the @include directive:

@include FileName.in
@include "file name with spaces.in"

The file name should include the path, either absolute or relative to the run-directory. The content of the file is included in the input at the point where the @include directive occurs. The @include directive may occur any number of times in the input.

The @include feature makes it easy to pack your preferred settings in one file and use them in every run with minimum input-typing effort.

Units¶

Some keys have a default unit associated (not all keys have units). For such keys, the default unit is mentioned in the key documentation. One can specify a different unit within square brackets at the end of the line:

KeyName value [unit]

For example, assuming the key EnergyThreshold has as default unit Hartree, then the following definitions are equivalent:

# Use defaults unit:
EnergyThreshold 1.0

# use eV as unit:
EnergyThreshold 27.211 [eV]

# use kcal/mol as unit:
EnergyThreshold 627.5 [kcal/mol]

# Hartree is the atomic unit of energy:
EnergyThreshold 1.0 [Hartree]

Available units:

• Energy: Hartree, Joule, eV, kJ/mol, kcal/mol, cm1, MHz

• Forces: Hartree/Bohr, eV/Bohr, Hartree/Angstrom, eV/Angstrom, kcal/mol/Angstrom, kJ/mol/Angstrom

• Length: Bohr, Angstrom, meter

• Angles: radian, degree

• Mass: el, proton, atomic, kg

• Pressure: atm, Pascal, GPa, a.u., bar, kbar

• Electric field: V/Angstrom, V/meter, a.u.