MOLPRO

17 THE DENSITY FUNCTIONAL PROGRAM 121
17.4.2 Implementing new functionals
New functionals are implemented based upon the automatic code generation (ACG) program
(doi:10.1016/S0010-4655(01)00148-5 ). In order to work the program requires the maple mathematics
program and an XSLT parser, defined by the variable XSLT in CONFIG.
The format of the input file is an XML file containing all of the information about the new
functional. All density functional XML files are placed in the directory lib/df and are automatically
activated on the next instance of the make command in the MOLPRO base directory.
The root element of the XML document is content. At the next level the element, functional
is expected, 1 per file.
The functional element has an id attribute which is used as the keyword for the functional
in MOLPRO, and optional doi attribute for specifying a reference. The allowed elements are
defined in table 8. The final element is maple for which multiple cases are allowed. A typical
title
tex
Text to appear as a heading for the functional documentation
Text to document the functional
maple expression such as
A:=1.2:
is written as
1.2.
To input a Maple procedure such as
Table 8: Elements allowed for defining functionals
add_together:=proc(a,b) a+b end:
one should write
a+b.
As an example the Perdew-Wang 1991 GGA exchange functional is given below:
Perdew-Wang 1991 GGA Exchange Functional
1/2*E(2*rho(s))
1/2*E(2*rho(s))
-3/(4*Pi)*(3*Piˆ2)ˆ(1/3)*nˆ(4/3)*F(S)
chi(s)/(2*(6*Piˆ2)ˆ(1/3))
(1+0.19645*S*arcsinh(7.7956*S) + (0.2743-0.1508*exp(-100*Sˆ2))*Sˆ2)/
(1+0.19645*S*arcsinh(7.7956*S)+0.004*Sˆ4)