[DFTB-Plus-User] N-H skf files

[Lin Song]

Dear DFTB+ users,

I’m confused which N-H skf file should I use, the mio-1-1 set or the miomod:nh set? My system is an enzyme and I’m using DFTB as the quantum method to do QM/MM MD studies in AMBER. Under the miomod:nh page, I found that it is modified to reproduce the sp3 nitrogen and proton affinity better, but the spa nitrogen are descibed correctly by the original mio-1-1 set. Now my system has both sp2 and sp3 nitrogen, should I use the original mio-1-1 set or the modified miomod:nh set? I appreciate any help! 

Following is the quote from the page under miomod:nh set:

In previous studies [JACS04,TCA06] consistent errors of about 10 kcal/mol were found specifically for proton affinities of sp3 hybridized nitrogen atoms. Therefore, a modified parameter set “NHmod” was introduced in which the N-H repulsive potential was shifted to correct for these errors. However, since sp2
hybridized nitrogen atoms seem to be described correctly, this correction has only to be applied for a certain electronic configuration of N. Therefore, similar to the situation in force fields, different “atom types” for N have to be introduced at the moment, which clearly limits DFTB’s applicability since these
atom types are not allowed to change during a reaction. For benchmarks see [JPCA07,JCTC11]. Geometrical properties are very similar to the original mio N-H parameter set.

Thanks,
Lin

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