Hello 
This difference is simply due to a sign convention on the energy: whether the system is doing work or having work done to it. The fact that the energy differences agree is a good indication that the calculations are consistent and the differences not relevant to most applications.
Thanks,

Nathan Baker
Laboratory Fellow and Technical Group Manager
Applied Statistics and Computational Modeling
Pacific Northwest National Laboratory
+15093753997
http://www.linkedin.com/in/nathanandrewbaker/
Original Message
From: Liu, Hanzhong [mailto:HLiu@...]
Sent: Wednesday, March 19, 2014 12:06
To: apbsusers@...
Subject: [apbsusers] sign of the totoal energy
Hi all:
I'm using APBS to calculate the polar solvation energy and comparing the result with the one calculated by Delphi. Following are my results.
APBS
Total energy in solution is 9.9 E+04 KJ/mol, total energy without solution (Coulombic interaction) is 1.0 E+05 KJ/mol, reaction filed energy is 4.1 E+03 KJ/mol
Delphi
Total energy in solution is 6.6 E+04 KJ/mol. total energy without solution (Coulombic interaction) is 6.2 E+04 KJ/mol, reaction field energy is 4.4 E+03 KJ/mol
Comparing these two results, the reaction field energy is pretty close. But in APBS, all the energy is positive. I've also checked outputs of given examples and these energies are all positive. If APBS gives an absolute value then the reaction field energy will be positive. I'm confusing about the sign of the total energy calculated in APBS.

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