Protocol threebody

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:

ΔE³ = E(ABC) - E(A) - E(B) - E(B) - ΔE²(AB) - ΔE²(BC) - ΔE²(CA)

What is, for practical calculations, it can be recasted in terms of energies as:

ΔE³ = E(ABC) - E(AB) - E(BC) - E(CA) + E(A) + E(B) + E(C)

Input structure

Optionally, following blocks can be defined in the input:

molecule_a - Definition of the first monomer (selection, charge, multiplicity)
molecule_b - Definition of the second monomer (selection, charge, multiplicity)
molecule_c - Definition of the third monomer (selection, charge, multiplicity)

Keywords used

Keywords specific for this protocol:

bsse_correction_3b

Other keywords used by this protocol:

Examples

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