Calculation of three-body contribution to the stabilization energy (the three-body energy) in a trimer. Basis set superposition error correction scheme where all subsystems are calculted in the trimer basis is applied by default but can be switched off. The setup for the monomers within the trimer is analogous to interaction energy calculations.
In a trimer ABC, it is defined as:
What is, for practical calculations, it can be recasted in terms of energies as:
The following examples, along with all other files needed to run them, can be found in the directory cuby4/protocols/threebody/examples
#=============================================================================== # Threebody energy calculation example 1 #=============================================================================== # Calculation of three-body energy in water trimer at SCC-DFTB level. # The monomers in the trimer are recognized automatically, for manual setup, # see Example 2 for protocol interaction. job: threebody # Switch off the default BSSE correction, it is not applicable at DFTB level bsse_correction_3b: none interface: dftb method: scc-dftb charge: 0 geometry: | O 0.000000 0.000000 0.000000 H 0.000000 0.000000 0.950000 H -0.895669 0.000000 -0.316667 O 0.000000 0.000000 3.000000 H 0.822724 0.000000 2.525000 H 0.173593 0.000000 3.934005 O 2.598076 0.000000 1.500000 H 1.775352 0.000000 1.025000 H 3.320152 0.000000 0.882662