Температура кипения

В википедии есть формула для определения температуры кипения:

Для воды у меня получилось:

# include "udf.h"

DEFINE_PROPERTY(saturation_temperature, c, t)
{
  return 1/(1/(273.15+100)-8.31*log(C_P(c,t)/101325)/40680);
}

График вполне допустимый (давление на нем в атмосферах)

Если задать зависимость таблицей в кусочно-линейном виде, то расчет идет, а по представленной формуле -- нет.

Выдает множество сообщений вида:

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k     epsilon  vf-phase-2     time/iter
     1  1.0000e+00  5.4653e-03  6.2700e-03  6.2487e-03  1.5195e-05  1.4033e+06  4.8634e+05  0.0000e+00  0:09:54   99
        Stabilizing pressure coupled using GMRES to enhance linear solver robustness.

Experiencing convergence difficulties - temporarily relaxing and trying again...
        Stabilizing pressure coupled using GMRES to enhance linear solver robustness.

Experiencing convergence difficulties - temporarily relaxing and trying again...
        Stabilizing pressure coupled using GMRES to enhance linear solver robustness.

Experiencing convergence difficulties - temporarily relaxing and trying again...
        Stabilizing pressure coupled using GMRES to enhance linear solver robustness.

Experiencing convergence difficulties - temporarily relaxing and trying again...
        Stabilizing pressure coupled using GMRES to enhance linear solver robustness.

Experiencing convergence difficulties - temporarily relaxing and trying again...

Divergence detected in AMG solver: pressure coupled
Divergence detected in AMG solver: pressure coupled
Divergence detected in AMG solver: pressure coupled
Divergence detected in AMG solver: pressure coupled
Error at host: floating point exception

===============Message from the Cortex Process================================

Compute processes interrupted. Processing can be resumed.

==============================================================================

Error at Node 0: floating point exception

Error at Node 2: floating point exception

Error at Node 3: floating point exception

Error at Node 1: floating point exception

Error: floating point exception
Error Object: #f

В чем именно моя ошибка?