7.2 Commands

A command invokes a particular program. It may be followed by local input for this program, enclosed in curley brackets¹

The general format is either

COMMAND, options

or

{ COMMAND,options
directives
data
}

Examples for commands are HF, MP2, CCSD(T), MCSCF, MRCI. Examples for directives are OCC, CLOSED, WF, PRINT. Directives can be in any order, unless otherwise noted. Data can follow certain directives. For the format of options, directives and data see subsections 3.3, 3.5, and 3.6, respectively.

In the following, such a sequence of input will be denoted a command block. Special command blocks are the geometry and basis blocks.

The options given on the command line may include any options relevant to the current program. For instance, in DF-LMP2-R12 this could be options for density fitting, local, explicit, and/or thresholds. Alternatively, options can be specified on individual directives like

DFIT,options
LOCAL,options
EXPLICIT,options
THRESH,options

In these cases, only the options belong to the corresponding directive are valid; thus, if an option for EXPLICIT would be specified, e.g., on the DFIT directive, an error would result. This error would be detected already in the input prechecking stage.

As already mentioned, the use of curly brackets is normally compulsary if more than one input line is needed. In the case of one-line commands, curley brackets are needed as well if the next command or procedure has the same name as a directive valid for the current command.

Note: DIRECT and associated options cannot be specified on command lines any more.