Academic literature on the topic 'RT-TDDFT'

Absorption spectra of 5-acene calculated using various functionals in RT-TDDFT. The subfigures (left top: LDA; left bottom: PBE; right: LB94) show the spectra close to the position of the ¹L_a and ¹L_b peaks, where the corresponding LR-TDDFT results are marked with the red lines.

The 2-(phenylazo)azobenzene furnished novel palladacycles in excellent yield, which showed luminescence at rt and catalytic activity. The optoelectronic and electrochemical responses were substantiated with DFT and TDDFT.

Using the linear combination of atomic orbitals real-time-propagation rt-TDDFT technique and transition contribution maps, we study the optical and plasmonic features of a metal nanoring made up of sodium atoms.

Three meso-substituted tetrapyridyl porphyrins (free base, Ni(ii), and Cu(ii)) were investigated for their optical limiting (OL) capabilities using real-time (RT-), linear-response (LR-), and quadratic-response (QR-) time-dependent density functional theory (TDDFT) methods.

Within the nuclear-electronic orbital (NEO) framework, the real-time NEO time-dependent density functional theory (RT-NEO-TDDFT) approach enables the simulation of coupled electronic-nuclear dynamics. In this approach, the electrons and quantum nuclei are propagated in time on the same footing. A relatively small time step is required to propagate the much faster electronic dynamics, thereby prohibiting the simulation of long-time nuclear quantum dynamics. Herein, the electronic Born–Oppenheimer (BO) approximation within the NEO framework is presented. In this approach, the electronic density is quenched to the ground state at each time step, and the real-time nuclear quantum dynamics is propagated on an instantaneous electronic ground state defined by both the classical nuclear geometry and the nonequilibrium quantum nuclear density. Because the electronic dynamics is no longer propagated, this approximation enables the use of an order-of-magnitude larger time step, thus greatly reducing the computational cost. Moreover, invoking the electronic BO approximation also fixes the unphysical asymmetric Rabi splitting observed in previous semiclassical RT-NEO-TDDFT simulations of vibrational polaritons even for small Rabi splitting, instead yielding a stable, symmetric Rabi splitting. For the intramolecular proton transfer in malonaldehyde, both RT-NEO-Ehrenfest dynamics and its BO counterpart can describe proton delocalization during the real-time nuclear quantum dynamics. Thus, the BO RT-NEO approach provides the foundation for a wide range of chemical and biological applications.

We investigate hole transfer in open carbynes, i.e., carbon atomic nanowires, using Real-Time Time-Dependent Density Functional Theory (RT-TDDFT). The nanowire is made of N carbon atoms. We use the functional B3LYP and the basis sets 3-21G, 6-31G*, cc-pVDZ, cc-pVTZ, cc-pVQZ. We also utilize a few Tight-Binding (TB) wire models, a very simple model with all sites equivalent and transfer integrals given by the Harrison ppπ expression (TBI) as well as a model with modified initial and final sites (TBImod) to take into account the presence of one or two or three hydrogen atoms at the edge sites. To achieve similar site occupations in cumulenes with those obtained by converged RT-TDDFT, TBImod is sufficient. However, to achieve similar frequency content of charge and dipole moment oscillations and similar coherent transfer rates, the TBImod transfer integrals have to be multiplied by a factor of four (TBImodt4times). An explanation for this is given. Full geometry optimization at the B3LYP/6-31G* level of theory shows that in cumulenes bond length alternation (BLA) is not strictly zero and is not constant, although it is symmetrical relative to the molecule center. BLA in cumulenic cases is much smaller than in polyynic cases, so, although not strictly, the separation to cumulenes and polyynes, approximately, holds. Vibrational analysis confirms that for N even all cumulenes with coplanar methylene end groups are stable, for N odd all cumulenes with perpendicular methylene end groups are stable, and the number of hydrogen atoms at the end groups is clearly seen in all cumulenic and polyynic cases. We calculate and discuss the Density Functional Theory (DFT) ground state energy of neutral molecules, the CDFT (Constrained DFT) “ground state energy” of molecules with a hole at one end group, energy spectra, density of states, energy gap, charge and dipole moment oscillations, mean over time probabilities to find the hole at each site, coherent transfer rates, and frequency content, in general. We also compare RT-TDDFT with TB results.

L'étude des interactions entre la lumière et la matière est devenue de plus en plus importante ces dernières années. Ceci est principalement dû au besoin croissant de nouveaux composés photoactifs dans diverses disciplines scientifiques, ce qui a conduit à une augmentation correspondante de l'utilisation de méthodes théoriques pour l'étude des états excités. Dans ce contexte, l'objectif de cette thèse est de contribuer au développement de nouveaux outils de calcul qui permettent une compréhension globale des mécanismes sous-jacents aux processus photoinduits. Ici, nous nous sommes concentrés sur la dynamique électronique ultrarapide des états excités par transfert de charge (CT) dans les molécules en utilisant la méthode « real-time time-dependent density functional theory » (RT-TDDFT). Bien que la TDDFT soit largement utilisée en raison de son efficacité, il est généralement reconnu que les états CT sont difficiles à décrire avec cette méthode en raison de la nature approximative des fonctionnelles utilisées pour calculer la contribution énergétique de l'échange et de la corrélation. Dans cette thèse, nous démontrons donc la relevance des descripteurs basés sur la densité dans le domaine de la dynamique des électrons en tant qu'outils pour caractériser la réponse ultrarapide de la densité et pour évaluer la fiabilité des simulations RT-TDDFT dans la description de la dynamique des états CT
The study of light-matter interactions has become increasingly important in recent years. This is mainly due to the growing need for innovative photoactive compounds in various scientific disciplines, which has led to a corresponding increase in the use of theoretical methods for the investigation of excited states. In this context, the objective of this thesis is to contribute to the development of novel computational tools allowing a comprehensive understanding of the mechanisms underlying photoinduced events. We focused on the ultrafast electron dynamics of excited states of charge transfer (CT) nature in molecules using Real Time - Time Dependent Density Functional Theory (RT-TDDFT). While TDDFT is widely used due to its good cost-accuracy ratio, it is generally recognized that CT states are indeed difficult to describe with this method due to the approximate nature of the functionals used to calculate the exchange and correlation energy contribution. In this work, we therefore demonstrate the relevance of density-based descriptors in the field of electron dynamics as tools to characterize the ultrafast density response and to assess the reliability of RT-TDDFT simulations in describing the dynamics of CT states

Le dommage d’irradiation dans la matière condensée est un phénomène important pour de nombreux domaines : les matériaux pour le nucléaire bien sûr, mais aussi l’électronique embarquée dans les satellites sujets aux rayonnements cosmiques, ou encore la matière vivante lors du traitement d’une tumeur par radiothérapie. Une connaissance précise de l’interaction entre la particule irradiante et le matériau cible est par conséquent fondamentale. L’interaction entre un projectile ionique et une cible peut être décrite par le biais du pouvoir d’arrêt. Il est défini comme étant le transfert d’énergie du projectile au matériau divisé par la profondeur d’implantation. La perte d’énergie d’un ion est induite majoritairement par les excitations électroniques de la cible. Le pouvoir d’arrêt électronique est alors la grandeur principale dans ce domaine. L’arrivée de la théorie de la fonctionnelle de la densité dépendante du temps (TDDFT) a permis d’améliorer largement la description de ce phénomène.Au cours de cette thèse, nous avons développé un code ab initio basé sur la TDDFT en temps réel (RT-TDDFT) dans les bases gaussiennes. Cette implémentation a des avantages considérables comme le traitement direct des électrons de cœurs, la rapidité de calculs des fonctionnelles hybrides et la flexibilité spatiale de la base. Avec notre code, nous avons vérifié la convergence du pouvoir d’arrêt vis-à-vis de la taille de la cible afin de tendre vers les matériaux cristallins. Nous avons analysé la dépendance du pouvoir d’arrêt en fonction du paramètre d’impact afin d’obtenir un pouvoir d’arrêt moyenné, correspondant aux conditions expérimentales. L’importance des excitations des électrons de cœurs dans l’irradiation ionique a été démontrée. Nous avons également étudié l’effet de la base gaussienne sur le pouvoir d’arrêt. Cette étude nous a permis de définir deux stratégies pour obtenir une bonne précision du pouvoir d’arrêt : l’extrapolation du pouvoir d’arrêt à partir des bases standards ou la génération de nouvelles bases.Finalement, nous avons calculé le pouvoir d’arrêt du lithium et de l’aluminium dans le cas de l’irradiation aux protons, aux antiprotons ainsi qu’aux particules alpha. Nous avons comparé nos résultats directement aux données expérimentales et aux données générées par le code empirique SRIM, largement utilisé par les expérimentateurs. Nous obtenons un bon accord avec SRIM lorsque celui-ci contient une base de données expérimentales suffisamment riche. De plus, nous avons observé l’effet de Barkas : le pouvoir d’arrêt des antiprotons est inférieur à celui des protons. Cet effet n’est pas reproduit dans les cas de théories plus simples telle que la théorie de la réponse linéaire
Ionic irradiation damage in condensed matter is central to many technological applications: materials in nuclear plants of course, but also electronics and solar panels in space that are subjected to the cosmic irradiation, living matter treated by radiotherapy to eliminate tumors, etc. For all these subjects, an accurate knowledge of the interaction between the irradiating projectile and the target is crucial. The interaction between the irradiating ion and the target material can be described by a stopping power, defined as the energy transfer from projectile to material per penetration distance. The most important ionic energy loss channels in the irradiation process are the electronic excitations. Therefore, the electronic stopping power is the central quantity in this field. With the advent of time-dependent density-functional theory (TDDFT), it is nowadays possible to provide a complete and realistic quantum-mechanical description of the phenomenon.In this thesis, we have developed a fully ab initio real-time TDDFT (RT-TDDFT) approach in the localized Gaussian basis. This implementation has several appealing advantages, such as the cheap account of core electrons, the ease of using the modern hybrid functionals, the flexibility of the basis set and overall low computational cost. With our tool, we explored the bulk limit, the validity of the projectile impact parameter averaging to obtain the experimental random electronic stopping power. We have proven the importance of core electron excitations in the ionic irradiations. A great care wasalso taken about the Gaussian basis set convergence: the extrapolation of the stopping power based on standard basis sets and the basis set generation scheme were proposed.Finally, we have computed the random electronic stopping power in lithium and aluminum targets for three types of projectiles: protons, antiprotons, and alpha-particles. We have compared our results directly to the experiment as well as to the empirical code SRIM, which is a widely-used database of stopping powers and a de facto standard for experimentalists. The agreement with SRIM is good when the SRIM database contains enough experimental points, whereas we show that the SRIM extrapolation can be hazardous when the underlying experimental data points are too few. Concerning the antiproton irradiation, our RT-TDDFT calculations show that the antiproton stopping power is lower than the proton one, which is in agreement with the general experimental observation (the so-called Barks effect). This effect is out of reach of simpler theories, such as the linear response approximation