3ob-3-1

This set of parameters is part of the Third-Order Parametrization for Organic and Biological Systems (3OB) has been specifically designed for Third Order Density Functional Tight Binding (DFTB3) and supersedes the mio parameter set. Main improvements over mio are improved geometries for non-covalent bonds as e.g. the hydrogen bond in the water dimer, a great reduction of the consistent overbinding and an overall improved performance. Comprehensive benchmark tests for C-H-N-O can be found in [JCTC2013], for P-S-* in [JCTC2014], for Mg-Zn-* in [JCTC2015-1], and for Na-F-K-Ca-Cl-Br-I-* in [JCTC2015-2].

When using this parameter set in DFTB+, make sure that

• you activate the third order correction by setting ThirdOrderFull = Yes
• you activate the damping of the Coulomb-interaction for hydrogen by setting HCorrection = Damping {
  Exponent = 4.00 }

The following zeta (Coulomb damping) parameter should be used for DFTB3 calculations (atomic units).

List of all atomic Hubbard derivatives (atomic units). Use the HubbardDerivs option in DFTB+ in order to specify them.

List of maximum angular momenta. Use the MaxAngularMomentum option in DFTB+ to specify them.

For the empirical halogend bond correction described in [JCTC2015-2]
the following parameters are provided:

DFTB3-D3(BJ) Parameters:
a1 = 0.746
a2 = 4.191
s8 = 3.209

General X-Correction parameters (AA and kcal/mol unit system):
c1 = 7.761
c2 = 0.050
c3 = 4.518

Element Pair Parameters (AA and kcal/mol unit system):
O-Cl = 1.237
O-Br = 1.099
O-I  = 1.313
N-Cl = 1.526
N-Br = 1.349
N-I  = 1.521
 

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