Input for ADF is structured by keywords, in short: keys. A key is a string of characters that does not contain a delimiter (blank, comma or equal sign). Keys are not case sensitive. Input is read until either the end-of-file condition (eof) becomes true, or until a record end input is encountered, whichever comes first. (end input is not a key.)
Key-controlled input occurs with two formats. In the first you have only one record, which contains both the key and - depending on the case - associated data: the key argument:
KEY argument
The whole part of the line that follows after the key is the argument. It may consist of more than one item.
The alternative format is a sequence of records, collectively denoted as a key block. The first record of the block gives the key (which may have an argument). The block is closed by a record containing (only) the word end. The other records in the block constitute the data block, and provide information related to the key.
KEY {argument}
data record
data record
...(etc.)...
...
end
In this manual, when items are optional, such as the argument in the scheme above, they are typed enclosed in curly brackets {}. The { and } characters themselves are not part of the item.
Block type keys may have subkeys in their data block. The subkeys may themselves also be block type keys. The data blocks of block type subkeys, however, do not end with end, but with subend:
KEY {argument}
data
data
subkey {argument}
subkey data
subkey data
...
subend
data
data
...
end
Layout features such as an open line, indentation, or the number of spaces between items are not significant.
The format to be used for a key is not optional: each admissible key corresponds to one specific format. As a general rule, the block keys control lists of data, such as atomic position coordinates.
A few special keys can have either format. For such keys the format actually in effect depends on the presence of the argument: the block type applies in absence of the argument. The block type applies also when an argument is present that ends with a continuation symbol. The continuation symbol is the ampersand (&) or, alternatively, two contiguous plus-characters preceded by at least one blank ( ++):
KEY {argument} &
data
data
end
The various types of keys are referred to respectively as simple keys, block keys, and general keys.
A considerable number of keys can be used to specify the geometry, the model Hamiltonian, cf. the Density Functional, the precision of the calculation, and so on. The order in which keys occur in the input file is immaterial, except that a few special keys determine how input data is interpreted, such as the unit-of-length for atomic coordinates. These interpretation keys must be used before the pertaining data in input occur. This will be mentioned explicitly again where they are discussed.
The items that can be addressed with keys and the keys themselves are listed in the Index.
Irrelevant keys, misspelling of keys
