Input Syntax

The input of deMon2k is easy and mnemonic and at the same time offers high flexibility. The input file contains keywords, options and keyword bodies. A keyword together with its options, and the keyword body forms a keyword block. The ordering of these blocks is free. The keyword body starts in a new input line directly after the keyword line(s), and must have the appropriate structure given in Chapter 4. All keywords, with the exception of GEOMETRY or its equivalent, REACTANT and PRODUCT, have associated default values which are used if the keyword is not explicitly specified in the input. Thus, the simplest deMon2k input contains only the coordinates of the atoms in the molecule to be calculated in the keyword body of GEOMETRY. deMon2k uses special symbols to make the keyword input flexible and efficient. Table 3 summarizes the special symbols that are allowed in the job input file deMon.inp.

Table 3: Special symbols of the deMon input.
Symbol Description
& Continuation of a keyword line
# First character of a comment line
= Assignment of numerical values to options
$ > $ Mathematical greater than symbol
$ < $ Mathematical smaller than symbol
^ Mathematical power symbol
- Combination of keyword options
Space Separation of keyword and options
, Separation of different options (optional)
END End of a keyword data block

Lines in the job input file deMon.inp are restricted to 80 characters. The input is not case sensitive. A keyword line can be continued by the & symbol at the very end of the line. At most, five continuation lines are permitted. The lines in the keyword body cannot be continued and, therefore, are limited to 80 characters. The TITLE line also cannot be continued and the length of the title string is restricted to 60 characters.

The symbol # indicates a comment line. Comment lines can occur only between complete keyword blocks including the keyword body, if it exists (Placing comments inside a keyword line or body results in unpredictable read operations). The end of a keyword block can be indicated by an END statement, by a comment symbol # in a new input line, or simply by a new keyword line.

Keyword options must be given directly after the keyword, separated by space(s). If options are not present, the default settings for them are used. Numerical values are assigned by the = sign to keyword options (e.g. SCFTYPE Tol = <Real>, where <Real> indicates a real number). The - sign is reserved for combining keyword options (e.g. VXCTYPE B88-LYP) where that is allowed. The other mathematical symbols in Table 3 are used according to their mathematical meaning. They can be surrounded by space(s).