Interface to the DFTB+ program implementing self consistenct charges density functional tight binding (SCC-DFTB) methods. The program requires also parameters available separately at www.dftb.org. Open source software.
Feb 2, 2016: two important changes were made in the input. Firstly, the built-in DFTB-D dispersion is now switched off by default. Warning is printed when the keyword is not set for a transition period. Secondly, the dftb_hubbard_derivs behaves differently and the default setup was changed to the values used in DFTB3.
Empirical dispersion coorrection was developed for SCC-DFTB with the MIO parameters set. It is available in DFTB+ and it can be activated by the dftb_dispersion keyword.
Since DFTB+ version 17.1, the D3 correction is available in the program. It is activated using the keyword dftb_d3. The damping is controlled by several keywords borrowed from the dispersion3 interface.
The acronym DFTB3 is used for a third-order SCC-DFTB with the 3OB parameter set and gamma function damping exponent of 4.0. The folowing input reproduces the DFTB3 setup in cuby:
method: scc-dftb3 dftb_slko_set: 3ob dftb_xh_damping: yes dftb_xh_damping_exp: 4.0
The D3 dispersion was parameterized for DFTB3 by Grimme, in Cuby it can be applied using the following setup:
modifiers: dispersion3 modifier_dispersion3: d3_damping: bj d3_a1: 0.746 d3_a2: 4.191 d3_s8: 3.209
In the latest release of DFTB+, the built-in D3 dispersion correction can be used; the results should be identical. The input is slightly different, the dispersion setup is passed directly to the dftb interface. The example abowe would change into:
method: scc-dftb3 dftb_slko_set: 3ob dftb_xh_damping: yes dftb_xh_damping_exp: 4.0 dftb_d3: yes d3_damping: bj d3_a1: 0.746 d3_a2: 4.191 d3_s8: 3.209
The most accurate description of non-covalent interactions in DFTB can be obtained with empirical corrections for both dispersion and hydrogen bonding. The latest version of the corrections was recently reparameterized for DFTB3, making the DFTB3-D3H4 method. Here, a different parameterization of the D3 dispersion is used which contains also a repulsive correction between hydrogens. The DFTB3-D3H4 calculation can be called using the following input:
method: scc-dftb3 dftb_slko_set: 3ob-3-1 modifiers: dispersion3, h_bonds4 # Dispersion3 setup modifier_dispersion3: d3_damping: :zero d3_sr6: 1.25 d3_alpha6: 29.61 d3_s8: 0.49 # Hydrogen-hydrogen repulsion: d3_hh_fix: yes d3_hh_para: :k: 0.30 :e: 14.31 :r0: 2.35 # H4 correction setup, including the additional # scaling for charged systems modifier_h_bonds4: h_bonds4_parameters: oh_o: 1.28 oh_n: 3.84 nh_o: 0.88 nh_n: 2.83 multiplier_wh_o: 1.00 multiplier_coo: 1.75 multiplier_nh4: 4.01 h_bonds4_extra_scaling: "@N&:hip": 3.44 "@N&:gua": 2.68
The following examples, along with all other files needed to run them, can be found in the directory cuby4/interfaces/dftb/examples
#=============================================================================== # DFTB example 1: energy calculation, configuration #=============================================================================== # SCC-DFTB calculation job: energy interface: dftb method: scc-dftb # Water molecule, geometry taken from Cuby's internal database geometry: A24:water charge: 0 #------------------------------------------------------------------------------- # Interface configuration #------------------------------------------------------------------------------- # DFTB+ executable dftbplus_exe: /home/rezac/bin/DFTB+/dftb+1.2.1/dftb+ # Path to directory containing directories with sets of Slater-Koster files dftb_slko_basepath: /home/rezac/bin/DFTB+/slko # Default set of Slater-Koster files (directory name) dftb_slko_set: mio-0-1 # In the following examples, it is assumed that this interface configuration # is performed in the config file
#=============================================================================== # DFTB example 2: Third-order SCC-DFTB #=============================================================================== # Third-order SCC-DFTB (also called DFTB3) calculation job: energy interface: dftb method: scc-dftb3 # Parameter set for DFTB3 - the 3OB set. The following keyword selects the # parameter set, the slater-koster files should be located in a directory # "3ob" under the path specified by the keyword dftb_slko_basepath (assumed) # to be set in the config file. dftb_slko_set: 3ob # Water molecule, geometry taken from Cuby's internal database geometry: A24:water charge: 0
#=============================================================================== # DFTB example 3: Use of external point charges #=============================================================================== # Geometry optimization of a water molecule in external electric field created # by two point charges along the x axis. In the optimization, the molecule # aligns with the field. job: optimize opt_quality: 0.1 interface: dftb method: scc-dftb geometry: | O 0.247000000 0.390000000 0.000000000 H -0.075000000 1.292000000 0.000000000 H 1.207000000 0.490000000 0.000000000 remove_translation: no remove_rotation: no # Allow rotation, by default both translational and rotational components of # the gradient are removed. point_charges: | 10.0 0.0 0.0 1.0 -10.0 0.0 0.0 -1.0 # A list of point charges, four numbers (x, y, z, charge) per line.