[gmx-users] Coulomb barriers and Coulomb Softcore Potential

Andreas Mecklenfeld a.mecklenfeld at tu-braunschweig.de
Mon Aug 24 15:55:45 CEST 2015

Dear Gromacs-Users,

I want to calculate the solvation free energy of water in an aqueous 
ionic solution and I'm using the Python tool "alchemical-analysis.py" by 
Klimovich, Shirts and Mobley for evaluation. This tool demonstrates a 
very high N/N_k ratio (up to 7000) while decreasing the electrostatic 
potential (Lennard Jones fully active).

Considering energetic barriers, I would like to adjust the Coulomb 
Softcore Potential. Does this seem plausible and if so, how is the 
Coulomb Softcore Potential defined in Gromacs?
Naden and Shirts provide a concept by equation (A.2) in "Linear Basis 
Function Approach to Efficient Alchemical Free Energy Calculations. 2. 
Inserting and Deleting Particles with Coulombic Interactions" 
(http://pubs.acs.org/doi/abs/10.1021/ct501047e) - is this the formula 

Best regards,

M. Sc. Andreas Mecklenfeld

Technische Universität Braunschweig
Institut für Thermodynamik
Hans-Sommer-Straße 5
38106 Braunschweig
Deutschland / Germany

Tel: +49 (0)531 391-2634
Fax: +49 (0)531 391-7814


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