Perple_X input files involve numerous linear functions of pressure and temperature (e.g.,
Margules parameters, van Laar size terms, DQF corrections, and enthalpy of ordering) of the
general form:
f = c_0 + c_T * T + c_P * P
Prior to the 6.7.3 version of Perple_X, when the coefficients were read, all three
coefficients were entered as in:
c_0 c_T c_P [DQF corrections in the thermodynamic data file make definitions]
DQF(A) = c_0 c_T c_P [DQF corrections in the solution model file]
W(A B) c_0 c_T c_P [Margules parameters in the solution model file]
a(A) c_0 c_T c_P [van Laar size terms in the solution model file]
... enthalpy = c_0 [enthalpy of ordering in the solution model file]
The 6.7.3 version of Perple_X reads these formats, but allows a more flexible format in
which c_T and c_P can be omitted if zero and tags are used to identify the coefficients
(meaning that users no longer need to remember the order in which the c_T and c_P
coefficients are entered; additional tags (e.g., '=' and '*') are also allowed. The general
format is (all on one line):
[name_tag] [=] c_0 [ [+/-] c_i [*] coefficient_tag]
where brackets indicate optional components and: +/- indicates a plus or minus sign; the
name_tag is prescribed for Margules parameters (e.g., W(A B)), van Laar size terms (e.g.,
a(A) and DQF corrections in the solution model file (e.g., DQF(A)); the = tag is mandatory
for enthalpy of ordering expressions; and the coefficient c_0 is mandatory in all input,
but, of course, may be zero; the coefficient tags must be < 9 characters and begin with an
upper or lower case T for the temperature coefficient. The coefficients may be rational
numbers (a) or fractions (a/b).
The text interpreter is fairly robust, but to be safe include a blank space before +/-
signs and after name and coefficient tags.
Examples of valid DQF function expressions in thermodynamic data file make definitions:
12d3 -0.14 1.
DQF(J/mol) = 0
DQF 1/2 -1*T_K
fudge_factor = 3 + 4*Pbar
Prior to the 6.7.3 the enthalpy of ordering term in solution models was assumed to be a
constant (c_0), it is now allowed linear pressure-temperature dependence.