Why this keyword is needed

In some complicated structures, particularly when several such structures are present in a single protein, the Lewis structure can only be constructed if various bonds are made or broken using keyword CVB. Editing long CVB  keywords can be difficult.  To make this task easier keyword "++" has been written.  All it does is to allow a single, long, keyword or SETUP line to be split into parts to simplify writing the long keyword line.  At run-time, the "++" will be used in reconstructing the long keyword line.

How to use "++"

Two "+" signs, i.e., "++" can be used to split a long keyword into parts that can be put on separate lines.  For example, in defining the bonds in the heme ring systems in oxy-hemoglobin the keyword:

CVB=("[HEM]1142:A.Fe":-"[HEM]1142:A.NA","[HEM]1142:A.Fe":-"[HEM]1142:A.NC","[HEM]1290:B.Fe":-"[HEM]1290:B.ND","[HEM]1290:B.Fe":-"[HEM]1290:B.NB","[HEM]1542:C.Fe":-"[HEM]1542:C.NB","[HEM]1542:C.Fe":-"[HEM]1542:C.ND","[HEM]1690:D.Fe":-"[HEM]1690:D.NB","[HEM]1690:D.Fe":-"[HEM]1690:D.ND","[HEM]1142:A.Fe":-"[OXY]1143:A.O1","FE HEM B1290":-"O2 OXY B1291","FE HEM C1542":-"O1 OXY C1543","[HEM]1690:D.Fe":-"O2 OXY D1691") setpi

is difficult to read and very difficult to debug.  But if "++" is used, then it can be rewritten as:

CVB=( ++
"[HEM]1142:A.Fe":-"[HEM]1142:A.NA", ++
"[HEM]1142:A.Fe":-"[HEM]1142:A.NC", ++
"[HEM]1290:B.Fe":-"[HEM]1290:B.ND", ++
"[HEM]1290:B.Fe":-"[HEM]1290:B.NB", ++
"[HEM]1542:C.Fe":-"[HEM]1542:C.NB", ++
"[HEM]1542:C.Fe":-"[HEM]1542:C.ND", ++
"[HEM]1690:D.Fe":-"[HEM]1690:D.NB", ++
"[HEM]1690:D.Fe":-"[HEM]1690:D.ND", ++
"[HEM]1142:A.Fe":-"[OXY]1143:A.O1", ++
"FE HEM B1290":-"O2 OXY B1291", ++
"FE HEM C1542":-"O1 OXY C1543", ++
"[HEM]1690:D.Fe":-"O2 OXY D1691") ++

When the job starts, each line ending in "++" has the following line joined to it, and the "++" is deleted. If "++" is used, and the next line starts with one or more spaces, these spaces will be preserved in the final keyword line.

WARNING! A common mistake is to have a "++" after a keyword ends and forget to add a space before the next keyword at the start of the following line.  If this happened, so the space was not present, the next keyword would be attached to the end of the last keyword on the line with the "++". An example of the correct use of this space can be seen in the space before "setpi" above.