Extension of the interacting quantum atoms (IQA) approach to B3LYP level density functional theory (DFT)

Abstract

An interaction between two atoms, bonded or non-bonded, consists of interatomic contributions: electrostatic energy, exchange energy and electronic correlation energy. Together with the intra-atomic energy of an atom, these contributions are the basic components of the Interacting Quantum Atom (IQA) energy decomposition scheme. Here, we investigate IQA's proper use in conjunction with an explicit implementation of the B3LYP functional. The recovery of the total molecular energy from the IQA components is emphasised, for the first time. A systematic study of three model systems of biological relevance, N-methylacetamide (NMA), the doubly capped tripeptide GlyGlyGly and an alloxan dimer, shows the stabilization effect of B3LYP on most of the interatomic exchange energies (V) compared to their Hartree-Fock values. Diagrams of exchange energies versus interatomic distance show the clustering of interactions, one cluster for each 1,n (n = 1 to 6 where the atoms are separated by n - 1 bonds). The positioning of some V values outside their expected cluster marks interesting interactions.

Perspective: Found in translation: Quantum chemical tools for grasping non-covalent interactions

“…The Interacting Quantum Atom (IQA) approach 174,175 partitions the energy components into intraatomic and interatomic terms by associating the terms of the one-and two-particle reduced density matrices (RDMs) with atomic basins. Moreover, the two-particle reduced density matrices are partitioned into Coulomb, exchange, and correlation terms, the latter of which is introduced through the use of a Kohn-Sham, 175,176 coupled-cluster, 177,178 CASSCF, or MP2 wavefunction. 174 Even though the energy partitioning in IQA is less clear-cut than SAPT (the physical interpretation of the correlation term is not as straightforward as the dispersion or …”

The prediction of topologically partitioned intra-atomic and inter-atomic energies by the machine learning method kriging

“…However, post-Hartree-Fock methods introduce a fourth (non-vanishing) contribution that is associated with electron correlation. In the current work, we use a version of IQA [41] that is compatible with DFT with an eye on including electron correlation effects. We invoke the use of DFT level with the largest of systems studied here, capped glycine.…”

Accurate prediction of the energetics of weakly bound complexes using the machine learning method kriging

“…Previously, IQA could only be used in conjunction with computational ansätze that generate a well-defined secondorder reduced density matrix. A recent publication explains the problem in greater detail [41] and presents a practical solution. An alternative, slightly more recent solution is that [42] of Francisco et al, which is not (yet) implemented in the software (see The GAIA Protocol) we used to generate the IQA contributions.…”

“…As a consequence of the widespread use of M06-2X, our group worked with Dr. Keith to have this functional implemented and tested in his program AIMAll. Using the same methodology thoroughly reported in our other research [41], the IQA decomposition can be performed on M06-2X wavefunctions. The other commonly available IQA theory levels (HF and B3LYP) would give poor interaction energies of weakly bound systems without the use of (ad hoc) dispersion corrections [56].…”