Interaction energies in noncovalent complexes, various decomposition schemes Prepared by Radek Marek group Interaction energy A B C A B Deformation energy Monomer geometry Geometry in a dimer Deformation (preparation) energy Binding (total) energy Basis sets • Set of functions representing atomic orbitals • Molecular orbital = linear combination of atomic orbitals (MO-LCAO) • Minimal basis set (one function per orbital) • Gaussian-type and Slater-type functions • 6-311++G(d,p) • LANL2DZ • aug-cc-pVTZ • Diffuse and polarization functions Formaldehyde in 3-21 basis set Pople and Dunning basis sets 3-21G(d,p) Dunning Gaussian-type Slater-type Anatomy of the Basis Set https://www.basissetexchange.org/ - Basis set exchange library Basis set vs. Accuracy Basis set superposition error (BSSE) Counterpoise (CP) method A B B A Ghost orbitals for monomers Practice1: counterpoise correction in Gaussian Water dimer from http://www.begdb.org/ web page, section “Water clusters – updated”, system name water-2-Cs Practice 1: Counterpoise correction in Gaussian: output Practice 1: Counterpoise (CP)-corrected interaction energy in Gaussian • Build any small non-covalent complex of your choice in Avogadro , GaussView or ChemCraft • Perform geometry optimization and frequency calculation at the RHF/6- 311G(d,p) computational level • Obtain counterpoise-corrected interaction energy and BSSE value for optimized geometry • Repeat the same procedure using RHF/3-21G computational level. How the geometry, interaction energy and BSSE values are different? • Visualize the output files in GaussView Energy decomposition analysis (EDA) Differential (deformation) density The positive values the point of density accumulation in the molecule (relative to isolated atoms). When the molecule is formed from atoms the density flows from the area of negative value towards the area with positive value The Natural Orbitals for Chemical Valence (NOCV) Practice 2: NH3 BH3 dative bond in the ammoniaborane • Build NH3BH3 molecule (shown by instructor) • Symmetrize the system by clicking on • Select Task → Geometry Optimization • Select XC functional → GGA:BP86 • Select Basis set → DZP • Select Numerical quality → Good • Run the calculation with File → Run (save with the name ammoniaborane) • After the geometry optimization is completed, Select Yes → New Job • Set Task → Single Point • Go in the panel bar to Model → Regions • Select the atoms of NH3 (holding Shift), click the + button, rename region to NH3, the same procedure for BH3 • Go in the panel bar to MultiLevel → Fragments • Check the ‘Use fragments’ check box • Properties → ETS-NOCV • Select an Closed-Shell ETS-NOCV analysis • EDA results and NOCV channels visualization (shown by instructor) • Homework: optimize NH3 and BH3 separately at the same computational level, find the total deformation energy Natural population analysis (NPA) NPA Natural bond orbitals Natural Bond Orbitals 2nd Order Perturbation Analysis of the Fock Matrix Practice 3: NBO analysis • Go to http://www.begdb.org/ • Download geometry of a non-covalent complex, e.g. A-T base pair in S22 - benchmark non-covalent complexes • Perform NBO analysis, B3LYP/6-311++G(d,p) computational level, add Pop=NBO output=wfn external="/software/ncbr/softrepo/ncbr/nbo“ to Gaussian root section • Analyze natural charges of atoms invoved in non-covalent interactions, NBOs and characteristic donor-acceptor interactions • Homework: try natural energy decomposition analysis for this complex