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Help with the Saturation Vapor pressure in CAM/CLM

Hi, I am using CAM 3 with the CLM (2 I believe) coupling.
I am trying to change the saturation vapor pressure equation (over ice) in the model to account for low temperatures, down to 120 K. I have the equation, and it works fine when I replaced the equation in CAM, but I have problems when I try to change the equation in the land model.

So far I have changed the equation in QSatMod.F90, and atmdrvMod.F90.
I wasn't able to find any other places where the equation is defined, so that's all I've changed so far. I also adjusted the input and output of the new equation so that the units match, so I don't think that's where the problem is.

Currently, the first error I recieve is a conservation error in dp_coupling and looks like:
dp_coupling cant adjust 1 51 11
9.999999999330256E-013 1.000000000000000E-012 3.424675268265322E-023

A number of other errors also follow concerning water conservation, and mixing ratio violaions. The model still runs for a while with these check failures, but it eventually fails. I also needed to reduce the model time step by a factor of 6 when I changed the equation in the land model, but I think this is related to the other issues, and hope that this is fixed when the other issues have been solved.
I am not sure if the problem arises from the fact that the vapor pressure becomes too small at these low temperatures, or if there are other places in the code that must be adjusted. Any help would be much appreciated.
 
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