3 research outputs found
Towards an Atomistic Understanding of Polymorphism in Molecular Solids
Many chemical
phenomena are ultimately due to energy balances between atoms. In order to
reach firm and clear conclusions one needs a reliable energy decomposition
analysis (EDA). The Interacting Quantum Atoms (IQA) energy partitioning method is one of the most
recent EDA methods. IQA is a topological energy partitioning that generates
well-defined intra- and interatomic contributions, of steric, electrostatic or
covalent (exchange) character. IQA has a minimal and powerful architecture and
does not suffer from a number of conceptual and practical problems that plague the more traditional non-topological EDAs
(Chem.
Soc. Rev., 44 (2015) 3177).For the first time,
our manuscript reports on a protocol for using the IQA to understand polymorphism,
which we apply to the three polymorphs of succinic acid (SA), including the
unusual polymorph that
was recently discovered serendipitously (CrystEngComm, 20 (2018) 3971). The many intra- and interatomic energy terms from the EDA scheme are processed using
a new technique that we developed called the Relative Energy Gradient (REG)
method, which clearly identifies the atoms and corresponding energetic terms
that govern the behaviour of the total system, in a minimal and unbiased way. </div
Multiconfiguration Pair-Density Functional Theory for Chromium(IV) Molecular Qubits
Pseudo-tetrahedral organometallic complexes containing chromium(IV) and aryl ligands have been experimentally identified as promising molecular qubit candidates. Here we present a computational protocol based on multiconfiguration pair-density functional theory for computing singlet-triplet gaps and zero-field splitting (ZFS) parameters in Cr(IV) aryl complexes. Notably, complete active space second-order perturbation theory (CASPT2) and hybrid multiconfiguration pair-density functional theory
(HMC-PDFT) perform better than Kohn-Sham density functional theory for singlet-triplet gaps. Despite the very small values of the ZFS parameters, all the examined multiconfigurational methods performed qualitatively well. CASPT2 and HMC-PDFT performed particularly well for predicting the trend in the ratio of the rhombic and axial ZFS parameters, |E/D|. We have also investigated the dependence and sensitivity of the calculated ZFS parameters on the active space and the procedure for geometry optimization. The methodologies outlined here will guide future prediction of ZFS parameters in molecular qubit candidates