Search results for "functional theory"
showing 10 items of 1012 documents
Stereoelectronic Properties of N-acetyl-α,β-dehydroamino acid N′-methylamides
1998
α,β-Dehydroamino acids are useful peptide modifiers. However, their stereoelectronic properties still remain insufficiently recognized. Based on FTIR experiments in the range of νs(N-H), AI, AII and νs(Cα=Cβ) and ab initio calculations with B3LYP/6-31G*, we studied the solution conformational preferences and the amide electron density perturbation of Ac-ΔXaa-NHMe, where ΔXaa = ΔAla, (E)-ΔAbu, (Z)-ΔAbu, (Z)-ΔLeu, (Z)-ΔPhe and ΔVal. Each of these dehydroamides adopts a C5 structure, which in Ac-ΔAla-NHMe is fully extended and accompanied by the strong C5 hydrogen bond. Interaction with bond Cα=Cβ lessens the amidic resonance within the flanking amide groups. The N-terminal C=O bond is noticea…
Growth of two-dimensional Au patches in graphene pores: A density-functional study
2017
Inspired by recent studies of various two-dimensional (2D) metals such as Au, Fe and Ag, we study the growth of two-dimensional gold patches in graphene pores by density-functional theory. We find that at room temperature gold atoms diffuse readily on top of both graphene and two-dimensional gold with energy barriers less than $0.5$ eV. Furthermore, gold atoms move without barriers from the top of graphene to its edge and from the top of 2D gold to its edge. The energy barriers are absent even at the interface of 2D gold and graphene, so that the gold atoms move effortlessly across the interface. We hope our demonstration for the propensity of diffusing gold atoms to grow 2D gold patches in…
Peptides as Versatile Platforms for Quantum Computing
2018
The pursuit of novel functional building blocks for the emerging field of quantum computing is one of the most appealing topics in the context of quantum technologies. Herein we showcase the urgency of introducing peptides as versatile platforms for quantum computing. In particular, we focus on lanthanide-binding tags, originally developed for the study of protein structure. We use pulsed electronic paramagnetic resonance to demonstrate quantum coherent oscillations in both neodymium and gadolinium peptidic qubits. Calculations based on density functional theory followed by a ligand field analysis indicate the possibility of influencing the nature of the spin qubit states by means of contro…
On the nature of parr functions to predict the most reactive sites along organic polar reactions
2013
Abstract Very recently, local electrophilic and nucleophilic “Parr functions” were empirically introduced (L.R. Domingo, P. Perez, J.A. Saez RSC Adv. 3 (2013) 1486) in order to properly characterize the most reactive sites along polar chemical reactions. This Letter reports a theoretical advance to the new methodology by identifying these quantities with key Fukui descriptors of the spin-polarized density functional theory . Given such framework properly incorporates the treatment of both charge-transfer and spin-polarization, this finding provides a significant insight and substantial step forward within the field of a chemical reactivity theory based on the conceptual framework of density…
Quantum chemistry of the excited state: 2005 overview
2005
The present contribution contains an overview of quantum-chemical methods and strategies to compute and interpret spectroscopic and photochemical phenomena in molecular systems. The state of the art for the quantum chemistry of the excited state is reviewed, focusing in the advantages and disadvantages of the most commonly employed computational methods, from the single configurational procedures like CI-Singles (CIS), propagator approaches, and Coupled-Cluster (CC) techniques, to the more sophisticated multiconfigurational treatments, with particular emphasis on perturbation theory, the CASPT2 approach. Also, a short summary on the performance, lights, and shadows of the popular TDDFT meth…
Ab initio simulation of (Ba,Sr)TiO3 and (Ba,Ca)TiO3 perovskite solid solutions
2019
This research was supported by the ERA-NET HarvEnPiez project. Many thanks to R. Dovesi, M.M. Kržmanc and D. Gryaznov for fruitful discussions.
Survival of Floquet–Bloch States in the Presence of Scattering
2021
Floquet theory has spawned many exciting possibilities for electronic structure control with light, with enormous potential for future applications. The experimental demonstration in solids, however, remains largely unrealized. In particular, the influence of scattering on the formation of Floquet-Bloch states remains poorly understood. Here we combine time- and angle-resolved photoemission spectroscopy with time-dependent density functional theory and a two-level model with relaxation to investigate the survival of Floquet-Bloch states in the presence of scattering. We find that Floquet-Bloch states will be destroyed if scattering-activated by electronic excitations-prevents the Bloch elec…
Interaction-induced spin polarization in quantum dots.
2010
The electronic states of lateral many electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb blockade peaks are measured. A zig-zag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by including the interaction effects within spin-density-functional theory a good agreement between experiment and theory is obtained. The absence of bimodality on Landau level 1 is found to be due to strong spin polarization.
Density functional theory calculations on magnetic properties of actinide compounds
2010
We have performed a detailed analysis of the magnetic (collinear and noncollinear) order and atomic and the electron structures of UO2, PuO2 and UN on the basis of density functional theory with the Hubbard electron correlation correction (DFT+U). We have shown that the 3-k magnetic structure of UO2 is the lowest in energy for the Hubbard parameter value of U=4.6 eV (and J=0.5 eV) consistent with experiments when Dudarev's formalism is used. In contrast to UO2, UN and PuO2 show no trend for a distortion towards rhombohedral structure and, thus, no complex 3-k magnetic structure is to be anticipated in these materials.
Redox potentials and acidity constants from density functional theory based molecular dynamics.
2014
CONSPECTUS: All-atom methods treat solute and solvent at the same level of electronic structure theory and statistical mechanics. All-atom computation of acidity constants (pKa) and redox potentials is still a challenge. In this Account, we review such a method combining density functional theory based molecular dynamics (DFTMD) and free energy perturbation (FEP) methods. The key computational tool is a FEP based method for reversible insertion of a proton or electron in a periodic DFTMD model system. The free energy of insertion (work function) is computed by thermodynamic integration of vertical energy gaps obtained from total energy differences. The problem of the loss of a physical refe…