Input
*****

The input options for Band are specified in a text file consisting of
a series of key-value pairs, possibly nested in blocks. The input is
usually embedded in an executable shell script. This is the content of
a typical shell script for running a Band calculation:

   #!/bin/sh

   $AMSBIN/ams <<eor
      # This is the beginning of the input.
      # The input consists of key-value pairs and blocks.
      # Here we define the input option for the AMS driver:

      Task GeometryOptimization

      System
         Atoms
            H 0.0 0.0 0.0
            H 0.9 0.0 0.0
         End
      End

      # Next comes the Band "Engine" block. The input options for Band, which are
      # described in this manual, should be specified in this block:

      Engine Band
         Basis
            Type DZP
         End

         XC
            GGA PBE
         End
      EndEngine
   eor

To run the calculation above from command-line you should:

1. Create a text file called, for example, "test.run" and copy-paste
   the content of the script above

2. Make the script executable by typing in your shell "chmod u+x
   test.run"

3. Execute the script and redirect the output to a file: "./test.run >
   out"

The program will create a directory called "ams.results". Inside it,
you will find the *logfile* "ams.log" (which can be used to monitor
the progress of the calculation) and the binary results files
"ams.rkf" and "band.rkf". After the calculation is completed, you can
examine the output file "out". For more details, see the AMS
documentation.

See also:

  The Examples section contains a large number of input examples.

Important:

  All options described in this manual should be specified in the Band
  Engine block:

     # All Band keywords should be specified inside the 'Engine Band' block
     Engine Band
        Basis
           Type DZP
        End

        XC
           GGA PBE
        End
     EndEngine


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 treated 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."
