This PhD thesis reports original research results concerning the development of theoretical models and computational protocols for the quantification and analysis of two of the most important quantum observables of open-shell systems: the electron spin density and the phosphorescence energy gap. In the first part, a comprehensive theory of the electron spin density topology is proposed for the first time [1]. Several new notions (spin density critical points, molecular spin graphs, spin density basins, spin maxima and spin minima joining paths etc.) and descriptors (local and integral spin polarization indeces, basin average spin density etc.) are introduced. This analysis reveals that the spin density topology, based on precise mathematical notions, can unveil precious information on the physical structure of spin-polarized systems. In particular, it enables to describe and quantify spin polarization and delocalization mechanisms and, at the same time, to evaluate the dependence of spin density distributions on the adopted level of theory. In the second part instead, the performance of the domain-based local pair natural orbital (DLPNO) variant of the “gold standard” CCSD(T) method for the prediction of phosphorescence energies of aromatic chromophores is investigated for the first time [2]. An extensive analysis of both accuracy and computational cost of the main parameters of the method (basis set, triples correction approximation, dimension of PNOs space) is conducted. Two procedures, the Gold DLPNO-CCSD(T) aimed at maximizing the accuracy and the Silver DLPNO-CCSD(T) aimed at minimizing the computational cost, which result in an excellent agreement with experimental data, are proposed. 1. G. Bruno, G. Macetti, L. Lo Presti and C. Gatti, “Spin Density Topology,” Molecules, 25, 3537, 2020. 2. G. Bruno, B. de Souza, F. Neese, and G. Bistoni, “Can domain-based local pair natural orbitals approaches accurately predict phosphorescence energies?,” Phys. Chem. Chem. Phys., 24, 14228–14241, 2022.

QUANTUM OBSERVABLES OF OPEN-SHELL SYSTEMS. A THEORETICAL STUDY / G. Bruno ; Tutor: L. Lo Presti, C. Gatti ; coordinatore: D. Passarella. - : . Dipartimento di Chimica, 2022. ((34. ciclo, Anno Accademico 2021.

QUANTUM OBSERVABLES OF OPEN-SHELL SYSTEMS. A THEORETICAL STUDY

G. Bruno
2022-09-16

Abstract

This PhD thesis reports original research results concerning the development of theoretical models and computational protocols for the quantification and analysis of two of the most important quantum observables of open-shell systems: the electron spin density and the phosphorescence energy gap. In the first part, a comprehensive theory of the electron spin density topology is proposed for the first time [1]. Several new notions (spin density critical points, molecular spin graphs, spin density basins, spin maxima and spin minima joining paths etc.) and descriptors (local and integral spin polarization indeces, basin average spin density etc.) are introduced. This analysis reveals that the spin density topology, based on precise mathematical notions, can unveil precious information on the physical structure of spin-polarized systems. In particular, it enables to describe and quantify spin polarization and delocalization mechanisms and, at the same time, to evaluate the dependence of spin density distributions on the adopted level of theory. In the second part instead, the performance of the domain-based local pair natural orbital (DLPNO) variant of the “gold standard” CCSD(T) method for the prediction of phosphorescence energies of aromatic chromophores is investigated for the first time [2]. An extensive analysis of both accuracy and computational cost of the main parameters of the method (basis set, triples correction approximation, dimension of PNOs space) is conducted. Two procedures, the Gold DLPNO-CCSD(T) aimed at maximizing the accuracy and the Silver DLPNO-CCSD(T) aimed at minimizing the computational cost, which result in an excellent agreement with experimental data, are proposed. 1. G. Bruno, G. Macetti, L. Lo Presti and C. Gatti, “Spin Density Topology,” Molecules, 25, 3537, 2020. 2. G. Bruno, B. de Souza, F. Neese, and G. Bistoni, “Can domain-based local pair natural orbitals approaches accurately predict phosphorescence energies?,” Phys. Chem. Chem. Phys., 24, 14228–14241, 2022.
LO PRESTI, LEONARDO
PASSARELLA, DANIELE
Open-shell systems; spin density; topology; quantum chemical topology; spin density critical points; spin maxima and minima joining paths; molecular spin graph; spin density basins; spin density source function; phosphorescence energy; aromatic chromophores; DLPNO-CCSD(T) method; TADF compounds.
Settore CHIM/02 - Chimica Fisica
https://doi.org/10.1039/D2CP01623K
https://www.mdpi.com/1420-3049/25/15/3537
QUANTUM OBSERVABLES OF OPEN-SHELL SYSTEMS. A THEORETICAL STUDY / G. Bruno ; Tutor: L. Lo Presti, C. Gatti ; coordinatore: D. Passarella. - : . Dipartimento di Chimica, 2022. ((34. ciclo, Anno Accademico 2021.
Doctoral Thesis
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Descrizione: First part of the thesis including the introduction and the results concerning the spin density topology
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phd_unimi_R12406_2.pdf

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Descrizione: Second part of the thesis concerning the theoretical investigation of phosphorescence energies of aromatic chromophores
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/936434
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