Stabilization of activated fragments by shell‐wise construction of an embedding environment

Abstract

An activated fragment which is structurally unstable when considered isolated can be stabilized through binding to a suitable molecular environment; for instance, to a transition-metal fragment. The metal fragment may be designed in a shell-wise build-up of a surrounding molecular environment. However, adding more and more atoms in a consecutive fashion soon leads to a combinatorial explosion of structures, which is unfeasible to handle without automation. Here, we present a fully automated and parallelized framework that constructs such an embedding environment atom-wise. Molecular realizations of such an environment are constructed based on simple heuristic rules intended to screen a sufficiently large portion of the possible compound space and are then subsequently optimized by electronic structure methods. (Constrained-optimized) structures are then evaluated with respect to a scoring function, for which we choose here the concept of gradient-driven molecule construction. This concept searches for structure modifications that reduce the forces on all atoms. We develop and analyze our approach at the example of CO activation by reproducing a known compound and mapping out possible alternative structures and their effect on the stabilization of a (bent) CO ligand. For all generated structures, the nuclear gradient on the activated fragment and its coordination energy are evaluated to steer the design process. © 2017 Wiley Periodicals, Inc.

Automated Selection of Active Orbital Spaces

“…Our result, however, agrees well with the DMRG study of Ref. 37 that also found a singlet ground state with a singlet-triplet splitting of 0.4 kcal/mol from a manually selected CAS (32,24). the different spin states.…”

“…After the active space selection, the orbitals were fully optimized in a DMRG (32,28)[1000]-SCF calculation. Figure 10 shows the relative energies of the six structures along the isomerization coordinate with the energy of the peroxo structure taken as a reference.…”

“…Scoring functions will be required to supply orbital selection criteria. For this purpose, natural orbital occupation numbers [5,[29][30][31][32] and entropy-based entanglement measures [33][34][35] defined with respect to individual orbitals can be employed. In this work, we show how a DMRG-based automated active orbital space selection can be accomplished.…”

“…CR-CCSD(TQ) L CAS(16,14)-SCF DMRG(48,36)[500]-SCF DMRG(32,28)[1000]-SCF#DMRG(48,36)[500]-SCF Relative energies of six isomers of Cu 2 O 2+ 2 (the energy of the peroxo structure taken as a reference) from calculations with different methods. The CR-CCSD(TQ) L and CAS(16,14)-SCF values were taken from Ref.12.…”

On the Problem of Multiple Minima on the S2 Excited Potential Energy Surface of Benzene: A Restricted Active Space Self Consistent Field Study

“…In the present work we have explored the S 2 potential energy surface (PES) of benzene by employing the Restricted Active Space Self-Consistent Field (RASSCF) method [20][21][22][23][24][25] which is a multireference wave function method describing ad-equately the mixing of electronic configurations and degeneracy effects and depicting very well the topology of the PESs. According to this method we choose an active space of the most important orbitals and then the initial space is partitioned into three subspaces called RAS1, RAS2 and RAS3.…”