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Calculation of complexation constant in water using firefly

Enrico
e.chiavazza@gmail.com

Hello to everyone,
I'm trying to estimate a trend in the complexation constant of sodium ion with several polycarboxylic ligand in water, i know that i should calculate the dG value of the complex from the G value of the reagents, i read several paper on which they explain the need of corrections that account for the solvatation contribution and for the thermal factor (in order to bring the system from 0 K to 298 K and 1 bar). In order to do that I've found the optimized structure of the participant molecule under PCM solvent modeling and than i run an hessian calculation to obtain the thermochemistry at RT but if i use the gibbs energy that i obtained from the thermochemistry i obtain a positive dG for the complex that do not reflect at all the experimental behavior so now i have some question to which i couldn't find an answer elsewhere:

- what is the correct energy value that i have to consider from the firefly output?
- what are the correct correction factor (Ezpe,Hcorr,Scorr,solvent) that i need to get a formally correct dG for the complexation reaction?

solved these basic issues, in your opinion is it better to take into account explicitly the first solvatation sphere of the sodium ion (6 water molecules)?

you can find attached a set of output file for the smaller complex of my serie,
thank you

EC

This message contains the 1298 kb attachment
[ IDA-Na_3-21G_DPCM.zip ] Output files for complexation reaction

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