Exploration of zeroth-order Wavefunctions and Energies for Intramolecular Symmetry-Adapted Perturbation Theory

Non-covalent interactions occur between and within all molecules and have a profound impact on structural and electronic phenomena in chemistry, biology, and material science. Understanding the nature of inter-and intramolecular interactions is essential not only for establishing the relation between structure and properties, but also for facilitating the rational design of molecules with targeted properties. These objectives have motivated the development of theoretical schemes decomposing intermolecular interactions into physically meaningful terms. Among the various existing energy decomposition schemes, Symmetry-Adapted Perturbation Theory (SAPT) is one of the most successful as it naturally decomposes the interaction energy into physical and intuitive terms. Unfortunately, analogous approaches for intramolecular energies are theoretically highly challenging and virtually nonexistent. Here, we introduce a zeroth-order wavefunction and energy, which represent the first step toward the development of an intramolecular variant of the SAPT formalism. The proposed energy expression is based on the Chemical Hamiltonian Approach (CHA), which relies upon an asymmetric interpretation of the electronic integrals. The orbitals are optimized with a non-hermitian Fock matrix based on two variants: one using orbitals strictly localized on individual fragments and the other using canonical (delocalized) orbitals. The zeroth-order wavefunction and energy expression are validated on a series of prototypical systems. The computed intramolecular interaction energies demonstrate that our approach combining the CHA with strictly localized orbitals achieves reasonable interaction energies and basis set dependence in addition to producing intuitive energy trends. Our zeroth-order wavefunction is the primary step fundamental to the derivation of any perturbation theory correction, which has the potential to truly transform our understanding and quantification of non-bonded intramolecular interactions. (C) 2014 AIP Publishing LLC.

Synthesis, Characterization, and Applications of Visible Light Active Metal-Organic Frameworks

Samantha Lynn Anderson

Understanding how crystalline materials are assembled is important for the rational design of metal-organic frameworks (MOFs). Controlling their formation can allow researchers to streamline the synthesis of new materials as well as control their properties for targeted applications. In the first chapter of this thesis we report the construction of two 3-dimensional TbIII based MOFs (SION-1 and SION-2). Here, SION-2 acts as a metastable MOF and intermediate phase that partially dissolves and transforms into the thermodynamically stable MOF, SION-1. This chemical transformation occurs in a DMF/water solvent mixture, and is triggered when additional energy is provided to the reaction. In situ studies reveal the partial dissolution of the metastable phase after which the MOF components are reassembled into the thermodynamically stable phase. The marked difference in thermal and chemical stability between the kinetically and thermodynamically controlled phases is contrasted by their identical chemical building unit composition. Following the understanding of this transformation, an isostructural family of SION-1 and SION-2 had been constructed using lanthanide metal salts, where LnIII-SION-1 is comprised of Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu and LnIII-SION-2 is formed using Ce, Nd, Eu, Gd, Tb and Yb. The electronic properties of lanthanide based MOFs have not been extensively studied due to the general cognizance that LnIII ions behave as isolated free ions as their 4f orbitals do not contribute to bonding. Here, we systematically studied the electronic properties (UV-vis) of LnIII-SION-1 and LnIII-SION-2 and show that the higher the intensity of this absorption band in LnIII-SION-1 is due to the better overlap between Ln(5d) and ligand(pi*) orbitals and reveals that the lowest unoccupied crystalline orbitals are dispersed over an energy range and can be considered as a conduction band. We validated this observation by the non-linear I-V curves collected on CeIII- and YbIII-SION-1, both of which display dielectric properties. In the second chapter of this thesis, we rationally design a novel biologically derived MOF featuring unobstructed Watson-Crick faces of Ade pointing towards the MOF cavities. We show, through a combined experimental and computational approach, that Thy molecules diffuse through the pores of the MOF and become base-paired with Ade. The Ade-Thy pair binding at 40-45% loading reveals that Thy molecules are packed within the channels in a way that fulfill both the Woodward-Hoffmann and Schmidt rules, and upon UV irradiation, Thy molecules dimerize into ThyThy. This study highlights the utility of MOFs as nanoreactors for the synthesis of molecules that are otherwise difficult. Concluding this thesis, a biologically derived multimodal sensor MOF is synthesized and a formed into a device. The MOF, SION-9, is comprised of Ade and a porphyrin based ligand, and has tuneable conductive properties ranged from 2.69-4.20 x 10-8 - 7.43-7.34 x 10-6 S/cm. SION-9 is sensitive to both pressure and temperature simultaneously, and demonstrated both fast response times (< 60 ms) and a long shelf life (> 6 months).

EPFL2019

Spectral properties of extended systems from Koopmans-compliant functionals

Riccardo De Gennaro

Electronic-structure simulations have been impacting the study of materials properties thanks to the simplicity of density-functional theory, a method that gives access to the ground state of the system. Although very important, ground-state properties represent just part of the information, and often technological applications rely more on excited-state properties. In the context of density-functional theory, the latter are difficult to extract and one usually has to resort to more sophisticated approaches. In the last years, Koopmans spectral functionals have emerged as an effective method which combines the feasibility of density-functional theory with the accuracy of more complex methods, such as many-body perturbation theory. While retaining its simplicity, Koopmans functionals extend the domain of density-functional theory providing direct access to charged excitations, and ultimately to the photoemission spectra of materials. This approach has been extensively employed in finite systems, displaying an accuracy which is comparable to that of state-of-the-art many-body perturbation theory methods. In extended systems, calculations were bound to the supercell (Gamma-only) method, preventing the access to the full band structure of the system. In this work we overcome this limitation, proving that a band structure description of the energy spectrum is possible, and providing a scheme to carry out calculations in crystalline materials. The first result of this work consists in proving the compliance of Koopmans functionals with the translation symmetry of the system. The validity of Bloch's theorem, thus the possibility of describing the spectrum via a band structure picture, depends on this condition. Because of the orbital-density-dependent nature of the functional, the invariance of the total energy with respect to unitary transformations of the one-electron orbitals is broken. The energy is then minimized by a particular set of orbitals, called ``variational'', which are strongly localized in space. In extended periodic systems, the localized, thus non-periodic, character of the variational orbitals is inherited by the effective orbital-density-dependent Hamiltonians, which apparently break the translation symmetry of the system. Here we show that, by requiring the variational orbitals to be Wannier functions, the translation symmetry is preserved and Bloch's theorem holds. In the second part, we devise a scheme to unfold the band structure from supercell (Gamma-only) calculations, and reconstruct the k-dependence of the quasiparticle energies. This method is then used to compute the band structures of a set of benchmark semiconductors and insulators. Finally, we describe a novel formulation of Koopmans functionals for extended periodic systems, which exploits from the beginning the translation properties of Wannier functions to realize a primitive cell-based implementation of Koopmans functionals. Results obtained from this second approach are also discussed. In the last part, we present the preliminary study of impurity states arising in crystalline materials in the presence of point defects.

EPFL2022

Spectral properties of extended systems from Koopmans-compliant functionals

Riccardo De Gennaro

EPFL2022

Synthesis, Characterization, and Applications of Visible Light Active Metal-Organic Frameworks

Samantha Lynn Anderson

EPFL2019