Time-dependent Density Functional Theory Approach Research Articles

Real-Time Simulation of Ultrafast Electronic Dynamics of Nanoscale Systems Involving an Organic Molecule and a Nanoparticle Dimer.

Understanding and predicting the behavior of nanomaterials composed of plasmons interacting with quantum emitters at ultrafast timescales is crucial for the better manipulation of light at the nanoscale and advancing technologies like ultrafast communication and computing. Here we perform a simulation of the "real-time" electronic dynamics of a coupled molecule-metal nanoparticle dimer interacting with an ultrashort resonant laser pulse by combining the real-time time-dependent density functional theory (RT-TDDFT) approach with the time-domain frequency-dependent fluctuating charge (TD-ωFQ) model, an atomistic electromagnetic (AEM) model for the dynamic plasmonic response of nanoparticles. It is shown that the induced dipoles evolve from an exponential decay pattern to a beat pattern with an increase in coupling strength, which is altered by changing the molecular orientation relative to the dimer axis. It is further shown that in the strong coupling regime, both the excited molecule and the plasmon relax rapidly due to the molecule-plasmon interaction, and the efficient coherent energy exchange between the interacting molecule and plasmon modes occurs on a femtosecond (fs) timescale. This work provides guidance on manipulating light-matter interaction and studying molecular plasmonics at extremely fast timescales.

Theoretical, structural, and electronic analyses of pyridin-based dyes for dye-sensitized solar cells applications.

The new series of donor-π-acceptor dyes have been designed using pyridine derivatives as a donor group and thienothiophene as a π-spacer group, which were linked via 10acceptor groups. The highest occupied molecular orbital energies range from - 6.177 to - 5.786eV, whereas the lowest unoccupied molecular orbital energies range from - 2.181 to - 3.664eV. A6 dye has smaller energy gap, lower hardness, higher electrophilicity index, and good photovoltaic performance than other sensitizers. The lowest dihedral angle is observed in A1, A2, A6, A7, and A8 which are appropriate for intramolecular charge transfer between the molecules. The A8 has higher light harvesting efficiency, which increases the photovoltaic efficiency of the designed dye. The A6, A7, and A8 dyes spend less time in the excited state, which means they emit photons more efficiently than other dyes. The interaction between donor to π-spacer (red line) parts of the dyes has the bonding interaction (positive), and π-spacer to acceptor (blue line) parts of the dyes have the bonding and antibonding (negative) behaviours. The dyes A5 and A9 have 305.79 and 357.71 times higher β0 values than urea (0.781 × 10-30 esu) molecules. The spectral properties of the A6 dye strongly affect the structural modification. The density functional theory (DFT) and time-dependent DFT (TD-DFT) approach B3LYP/6-311G (d,p) basic set were used to optimize the designed dyes. All the calculations are performed using Gauss view 6.0 and Gaussian 09 software. The density of state spectrum is plotted using Gauss sum 2.6.

Time-dependent Kohn-Sham electron dynamics coupled with nonequilibrium plasmonic response via atomistic electromagnetic model.

Computational modeling of plasmon-mediated molecular photophysical and photochemical behaviors can help us better understand and tune the bound molecular properties and reactivity and make better decisions to design and control nanostructures. However, computational investigations of coupled plasmon-molecule systems are challenging due to the lack of accurate and efficient protocols to simulate these systems. Here, we present a hybrid scheme by combining the real-time time-dependent density functional theory (RT-TDDFT) approach with the time-domain frequency dependent fluctuating charge (TD-ωFQ) model. At first, we transform ωFQ in the frequency-domain, an atomistic electromagnetic model for the plasmonic response of plasmonic metal nanoparticles (PMNPs), into the time-domain and derive its equation-of-motion formulation. The TD-ωFQ introduces the nonequilibrium plasmonic response of PMNPs and atomistic interactions to the electronic excitation of the quantum mechanical (QM) region. Then, we combine TD-ωFQ with RT-TDDFT. The derived RT-TDDFT/TD-ωFQ scheme allows us to effectively simulate the plasmon-mediated "real-time" electronic dynamics and even the coupled electron-nuclear dynamics by combining them with the nuclear dynamics approaches. As a first application of the RT-TDDFT/TD-ωFQ method, we study the nonradiative decay rate and plasmon-enhanced absorption spectra of two small molecules in the proximity of sodium MNPs. Thanks to the atomistic nature of the ωFQ model, the edge effect of MNP on absorption enhancement has also been investigated and unveiled.

Influence of Solvents and Halogenation on ESIPT of Benzimidazole Derivatives for Designing Turn-on Fluorescence Probes.

This work reports a theoretical investigation of the solvent polarity as well as the halogenation of benzimidazole derivatives during excited state intramolecular proton transfer (ESIPT). It details how the environment and halogen substitution may contribute to the efficiency of ESIPT upon keto-enol tautomerism and exploits this effect to design fluorescence sensing. For this purpose, we first examine the conformational equilibrium of benzimidazole derivatives containing different halogen atoms, which results in intramolecular proton transfer, using density-functional theory (DFT) combined with the polarizable continuum model (PCM). Then we evaluate the fluorescence of the benzimidazole derivatives in different dielectric constants within time-dependent DFT (TD-DFT) approaches. Our results quantitatively allow the determination of large Stokes shifts in nonpolar solvents around 100 nm. These theoretical results are in agreement with experimental solvatochromism studies of benzimidazoles. The effect of halogenation, with fluorine, chlorine, and bromine, is less important than solvent polarization when ESIPT takes place. Thus, halogenation can be properly chosen depending on the interest of the synthesis of benzimidazole-based turn-on fluorescence in appropriate solvents.

Orbital-Optimized Versus Time-Dependent Density Functional Calculations of Intramolecular Charge Transfer Excited States.

The performance of time-independent, orbital-optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital-optimized calculations, even when including orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. -2 eV for TD-DFT, no correlation is observed for the orbital-optimized approach. The orbital-optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with a long-range charge transfer character. Orbital-optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best-performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.

Exploration of promising photovoltaic properties of bisisoindigo-based heterocyclic chromophores for organic solar cells: A DFT/TD-DFT study

In the current study, a series of A1–π–A2–π–A1 type bisisoindigo-based organic compounds (BTIND1–BTIND9) were designed via the structural tailoring of the reference compound (BTINR) at terminal acceptors for the organic solar cells (OSCs). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches were utilized to estimate the influence of end-capped engineering over their photovoltaic properties of BTIND1–BTIND9. After their structural optimization, various analyses like, open circuit voltage (Voc), absorption spectra (λmax), frontier molecular orbitals (FMOs), density of states (DOS), binding energy (Eb) and transition density matrix (TDM) were performed at the B3LYP/6-311G(d,p) level. The band gaps range of the engineered molecules was observed as 1.776–1.649 eV, lesser than the BTINR reference (1.812 eV). Their TDM and DOS details further revealed electronic charge transfer in the designed derivatives. The higher λmax values were found in the visible and near-infrared regions i.e., 666.904–701.149 nm in the chloroform solvent and 661.778–895.581 nm in the gaseous phase. Furthermore, their open-circuit voltage (Voc) was determined with PTB7 donor polymer and showed significant values. Among all, BTIND5, BTIND7 and BTIND8 compounds were investigated with remarkable photovoltaic properties. These chromophores possessed least energy gaps (1.649, 1.668 and 1.664 eV) and bathochromic shifts (698.070, 699.646 and 701.149 nm) with least binding energies and prominent Voc results. The above-mentioned outcomes demonstrate that the end-capped modification of bisisoindigo-based molecule is an effective strategy to obtain highly efficient OSCs.

Effect of spirocyclization of xanthene dyes on linear and nonlinear optical properties by considering D-π-A and D-A-D Systems: DFT and TD-DFT approach

Spirocyclization, a unique feature of xanthene dyes, makes it a promising candidate for developing fluorescent ratiometric probes for sensing, imaging, tracking, and labeling. How will this feature of xanthene dyes influence the linear and nonlinear optical properties? To examine the effect of spirocyclization of xanthene dyes, we have selected both the open-close form of rhodamine B and π-extended xanthene dyes substituted with thienyl and thieno[3,2-b]thienyl group at position 3 and 6. Here, rhodamine B will serve as the (Donor)D-π-A(Acceptor) system and thiophene-substituted xanthene dyes will serve as the D-A-D system. The geometry optimization of the close-open form of xanthene dyes at B3LYP/6–311++G(d,p) and CAM-B3LYP/6–311++G(d,p) revealed that the open form is energetically more stable in the S0 state than the closed form. The vertical excitation energy (ΔE), from Time-Dependent-Density Functional Theory (TD-DFT) calculation at B3LYP/6–311++G(d,p), CAM-B3LYP/6–311++G(d,p), ωB97XD/6–311++G(d,p) revealed that (ΔE)open < (ΔE)close. Further, the open form of xanthene dyes displays red-shifted absorption compared to the closed form. The λVt of xanthene dyes (open-close forms) is mainly assigned to HOMO → LUMO transition (S0 → S1) with % orbital contribution for open form ∼ 90 % and close form ∼ 60 %. The oscillator strength of xanthene dyes is obtained in the range of 0.01 – 1.74. The λVt of xanthene dyes is in agreement with experimental absorption. The static polarizability (α0), first-order hyperpolarizability (β0), second-order hyperpolarizability (γ), molecular hyperpolarizability (µβ0), and frequency-dependent hyperpolarizability (β1064), of the open form of xanthene dyes, were found to be higher than the close form. Thus, the open form of xanthene dyes will show superior linear and nonlinear optical properties than the closed form. The thienyl[3, 2-b] thieno substituted xanthene dye with red-shifted absorption shows higher α0, β0, γ, µβ0, β1064, and γ values, show better linear and NLO properties than thienyl and diethylamine substituted xanthene dyes.

Synthesis, solvent role, absorption and emission studies of cytosine derivative

The (E)-4-((4-hydroxy-3-methoxy-5-nitrobenzylidene) amino) pyrimidin-2(1H)-one (C5NV) was synthesized from cytosine and 5-nitrovanilline by simple straightforward condensation reaction. The structural characteristics of the compound was determined and optimized by WB97XD/cc-pVDZ basis set. The vibrational frequencies were computed and subsequently compared to the experimental frequencies. We investiated the electronic properties of the synthesized compound in gas and solvent phases using the time-dependent density functional theory (TD-DFT) approach, and compared them to experimental values. The fluorescence study showed three different wavelengths indicating the nature of the optical material properties. Frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) analyses were conducted for the title compound, and electron localized functions (ELF) and localized orbital locators (LOL) were used to identify the orbital positions of localized and delocalized atoms. Non-covalent interactions (H-bond interactions) were investigated using reduced density gradients (RDGs). The objective of the study was to determine the physical, chemical, and biological properties of the C5NV. The molecular docking study was conducted between C5NV and 2XNF protein, its lowest binding energy score is −7.92 kcal/mol.

Adjusting UV-Vis Spectrum of Alizarin by Insertion of Auxochromes.

First synthesized in 1868, alizarin became one of the first synthetic dyes and was widely used as a red dye in the textile industry, making it more affordable and readily available than the traditional red dyes derived from natural sources. Despite extensive both experimental and computational analyses on the electronic effects of substituents on the shape of the visible spectrum of alizarin and alizarin Red S, no previous systematic work has been undertaken with the aim to fine tune the dominant absorption region defining its color by introducing other electron-withdrawing or electron-donor groups. For such, we have performed a comprehensive study of electronic effects of substituents in position C3 of alizarin by means of a time dependent DFT approach. These auxochromes attached to the chromophore are proven to alter both the wavelength and intensity of absorption. It is shown that the introduction of an electron-donor group in alizarin causes the transition bands to be significantly red-shifted whereas electron-withdrawing groups cause a minor blue-shifting.

Geometrical factor, bond order analysis, vibrational energies, electronic properties (gas and solvent phases), topological and molecular docking analysis on Ipriflavone-osteoporosis diseases

Abstract In this research project, a computational assessment of the molecular structure of Ipriflavone (IP) in the gaseous phase was done based on density functional theory (DFT). In the realm of theory, the standard basis set B3LYP is a collection of functions used with linear combinations to produce molecular orbitals, making it simple to compute the molecular structure related to the given compound. With the time-dependent DFT approach, the UV spectra obtained for various solvents were used for examining the electronic transport features. A three-dimensional representation of the molecules that shows the charge distributions and charge-related characteristics of the molecule has the acronym the electrostatic potential map. The frontier molecular orbitals (FMO) confirmed the compound’s stability and good reactivity. Hyperpolarizability calculations were performed with good non-linear optical (NLO) potent. Natural bond orbital (NBO) analysis was used to explore charge delocalization and the compound’s stability. Topological investigations have been identified to clarify the bonding zones, weakest contacts, and electron energy density. Drug likeness studies were used to promote bioactivities. The outcome of docking tests shows that the ligand under investigation is beneficial at preventing bone loss-osteoporosis. To sum up, this work provides a comprehensive analysis that combines spectroscopic and quantum computational techniques to assess the effect of specific medicinal compounds on solvation and metabolic activity. Strategies for subsequent studies can thus greatly benefit from the knowledge obtained.

Structural tailoring via end-capped acceptors of thiophene-based C-shaped non-fullerene compounds with A-π-A backbone for the exploration of photovoltaic response

In the current era, non-fullerene based electron acceptors show remarkable contribution to develop organic solar cells (OSCs) with maximum possible efficiency via improving their optoelectronic properties. Thus, in current report, eight novel A-π-A type dithieno[3,2-b:2′,3′-d]thiophene (DTh) core-based C-shaped non-fullerene acceptors (ETMM1–ETMM8) were designed theoretically by taking ETMMR as reference to achieve highly proficient photovoltaic materials. Hence, a comprehensive density functional theory (DFT) analysis was accomplished by employing B3LYP level in conjunction with 6-311G(d,p) basis set to determine the enhancement of optical as well as photochemical response. Whereas time-dependent density functional theory (TD-DFT) approach was used for excited state calculations of all the investigated chromophores (ETMMR and ETMM1–ETMM8). So, the influence of structural tailoring via end-capped acceptors modifications was explored by utilizing various quantum chemical analyses such as: transition density matrix (TDM), HOMO–LUMO band gap, density of states (DOS), UV–Vis, binding energy (Eb), global reactivity parameters (GRPs), molecular electrostatic potential (MEP) and open circuit voltage (Voc). Remarkably, all the derivatives (ETMM1–ETMM8) exhibited comparable results with that of the reference chromophore (ETMMR). The results of UV–Vis analysis in chloroform solvent fall in the following order for all the modified chromophores: ETMM5 > ETMM3 > ETMM8 > ETMM4 > ETMM7 > ETMM2 > ETMM6 > ETMM1, which demonstrated maximum red shift in ETMM5 (785.257 eV). Fascinatingly, lowest excitation energy (1.579 eV) as well as binding energy (0.319 eV) along with minimum HOMO/LUMO band gap (1.898 eV) suggested ETMM5 as an excellent candidate for high performance OSCs. Concludingly, all the results indicated that modification of end-capped acceptors is an effective alternative approach to obtain desirable optoelectronic properties.

Wigner-Seitz truncated time-dependent density functional theory approach for the calculation of exciton binding energies in solids

Wigner-Seitz truncated time-dependent density functional theory approach for the calculation of exciton binding energies in solids

A theoretical study of ferrocene based on combined configuration interaction singles (CIS) and time-dependent density functional theory (TDDFT) approach

The state-of-the art density functional theory (DFT) is used to clearly resolve the two parallel cyclopentadienyl rings of ferrocene, which are either staggered (D5d symmetry) or eclipsed (D5h symmetry), in their ground-state conformation. Present result revealed that the eclipsed conformer with D5h point group represents the true minimum ground state structure of ferrocene. Natural population analysis is used to determine how atomic charge is distributed across different atoms of ferrocene D5h conformer and also the distribution of electrons in the core, valence, and Rydberg sub-shells. It is further investigated in potential energy scan that the rotation of the dihedral angle δ from 0° to 3π/5 will reproduce three times D5h or D5d conformers periodically as the period of 2π/5 due to the pentagonal structure of the CP ring. Further to examine optical spectra in the ultraviolet-visible (UV–vis) range, configuration interaction single (CIS) and time-dependent density functional theory (TDDFT) have conducted which help in locating the significant electronic shifts between different energy levels. Absorption spectra for high spin states were also generated in order to comprehend the characteristics of low-lying spin excitation. According to our estimates, the greatest absorption intensity is restricted to an energy range of 4–6 eV. Knowledge of ferrocene conformers will improve the research on other metallocenes and their derivatives, which have applications in biotechnology, nanotechnology, and solar technology.

Cost-Effective Approach for Modeling of Multiresonant Thermally Activated Delayed Fluorescence Emitters.

Multiresonant thermally activated delayed fluorescence (MR-TADF) emitters have recently attracted great interest for application in organic light-emitting diodes due to their remarkable electroluminescent efficiency and narrow emission spectra. It is therefore essential to establish computational methodologies that can accurately model the excited states of these materials at manageable computational costs. With regard to MR-TADF design and their associated photophysics, previous works have highlighted the importance of wave function-based methods, at much higher computational costs, over the traditional time-dependent density functional theory approach. Herein, we employ two independent techniques built on different quantum mechanical frameworks, highly correlated wave function-based STEOM-DLPNO-CCSD and range-separated double hybrid density functional, TD-B2PLYP, to investigate their performance in predicting the excited state energies in MR-TADF emitters. We demonstrate a remarkable mean absolute deviation (MAD) of ∼0.06 eV in predicting ΔEST compared to experimental measurements across a large pool of chemically diverse MR-TADF molecules. Furthermore, both methods yield superior MAD in estimating S1 and T1 energies over earlier reported SCS-CC2 computed values [J. Chem. Theory Comput. 2022, 18, 4903]. The short-range charge-transfer nature of low-lying excited states and narrow fwhm values, hallmarks of this class of emitters, are precisely captured by both approaches. Finally, we show the transferability and robustness of these methods in estimating rates of radiative and nonradiative events with adequate agreement against experimental measurements. Implementing these cost-effective computational approaches is poised to streamline the identification and evaluation of potential MR-TADF emitters, significantly reducing the reliance on costly laboratory synthesis and characterization processes.

Cluster-Based Approach Utilizing Optimally Tuned TD-DFT to Calculate Absorption Spectra of Organic Semiconductor Thin Films.

The photophysics of organic semiconductor (OSC) thin films or crystals has garnered significant attention in recent years since a comprehensive theoretical understanding of the various processes occurring upon photoexcitation is crucial for assessing the efficiency of OSC materials. To date, research in this area has relied on methods using Frenkel-Holstein Hamiltonians, calculations of the GW-Bethe-Salpeter equation with periodic boundaries, or cluster-based approaches using quantum chemical methods, with each of the three approaches having distinct advantages and disadvantages. In this work, we introduce an optimally tuned, range-separated time-dependent density functional theory approach to accurately reproduce the total and polarization-resolved absorption spectra of pentacene, tetracene, and perylene thin films, all representative OSC materials. Our approach achieves excellent agreement with experimental data (mostly ≤0.1 eV) when combined with the utilization of clusters comprising multiple monomers and a standard polarizable continuum model to simulate the thin-film environment. Our protocol therefore addresses a major drawback of cluster-based approaches and makes them attractive tools for OSC investigations. Its key advantages include its independence from external, system-specific fitting parameters and its straightforward application with well-known quantum chemical program codes. It demonstrates how chemical intuition can help to reduce computational cost and still arrive at chemically meaningful and almost quantitative results.

Effects of Oxygen Adsorption on the Optical Properties of Ag Nanoparticles.

Plasmonic metal nanoparticles are efficient light harvesters with a myriad of sensing- and energy-related applications. For such applications, the optical properties of nanoparticles of metals such as Cu, Ag, and Au can be tuned by controlling the composition, particle size, and shape, but less is known about the effects of oxidation on the plasmon resonances. In this work, we elucidate the effects of O adsorption on the optical properties of Ag particles by evaluating the thermodynamic properties of O-decorated Ag particles with calculations based on the density functional theory and subsequently computing the photoabsorption spectra with a computationally efficient time-dependent density functional theory approach. We identify stable Ag nanoparticle structures with oxidized edges and a quenching of the plasmonic character of the metal particles upon oxidation and trace back this effect to the sp orbitals (or bands) of Ag particles being involved both in the plasmonic excitation and in the hybridization to form bonds with the adsorbed O atoms. Our work has important implications for the understanding and application of plasmonic metal nanoparticles and plasmon-mediated processes under oxidizing environments.

A combined theoretical and experimental study of nickel derivative [Daiquiris(nicotinamide-jN1)nickel (II)]-lfumarato-K2O1:O4

The ground state geometry of the nickel derivative [Daiquiris(nicotinamide-jN1) nickel(II)]-fumarato-K2O1:O4 has been optimized and is being led toward its quantum chemical analysis in this paper. For more accuracy, we used the 6-311[Formula: see text]G (d, p) basis set for C, H, N, and O atoms and the LAN2DZ basis set for Ni. The calculated and experimental infrared (IR) spectra for the title molecule are well correlated, and the correlation factor [Formula: see text] shows that the method effectively interprets the molecule’s IR spectra. The electronic properties such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies and associated energy gap have been calculated by Time-Dependent Density Functional Theory (TD-DFT) approach. The natural bond orbital (NBO) analysis of the molecule describes how interatomic charge transfer results in the formation of bonding–nonbonding interactions. The experimental and calculated Ultraviolet visible (UV-Vis) spectra are compared. We anticipate our work will inspire fresh approaches to the title molecule’s ongoing research.

Synthesis, Computational and Antimicrobial Study of 2-(2-Hydrazinyl)thiazole Derivatives

In the present investigation, we report a combined computational and experimental study of eight thiazole derivatives (4a-4h) obtained from 3,4-dihydronaphthalen-1(2H)-one. A green chemistry protocol comprising PEG-400 and sulfamic acid was employed for the synthesis of eight diverse thiazole derivatives from 3,4-dihydronaphthalen-1(2H)-one, thiosemicarbazide and various phenacyl bromides. The synthetic strategy provides benefits like short reaction time, high yield, and non-chromatographic purification. The compounds were structurally confirmed on the basis of IR, 1HNMR and 13C NMR. The obtained thiazole derivatives were studied using the density functional theory (DFT) method employing B3LYP/6-311G(d,p) level of theory for optimization and Time-Dependent DFT (TD-DFT) approach for examining electronic energies and UV-Vis characteristics. Various computational parameters like bond length, bond angles, HOMO, LUMO, MESP, Mulliken charges, and global descriptors are obtained and discussed. The UV-Vis study the in gas phase and DMSO solvent was investigated to obtain various insights such as absorption energies oscillator strength, configurations and transitions of examined thiazole derivatives. The effect of polar solvent has augmented the absorption wavelength of all studied thiazole derivatives. The experimental and simulated UV-Vis data correlate with each other prompting the effectiveness of the computed method. The scaled and experimental wavenumbers provided the appropriate assignment of various vibrational signals. The antibacterial study was performed against E. coli, P. aeruginosa, and S. aureus which demonstrated the strong antibacterial potential against S. aureus. The antifungal study against C. albicans revealed that these compounds are poor antifungal agents. The DPPH and OH radical assays were used to establish the % radical scavenger effects and results showed that these derivatives are good antioxidant agents. The % hemolytic activity of the tested compounds showed that all compounds fall within the acceptable toxicity limit. Importantly in slico ADME and toxicity prediction studies of these compounds highlighted good ADME profile with no hepatotoxicity, immunotoxicity and cytotoxicity.

Nuclear-Electronic Orbital Quantum Mechanical/Molecular Mechanical Real-Time Dynamics.

Simulating the nuclear-electronic quantum dynamics of large-scale molecular systems in the condensed phase is key for studying biologically and chemically important processes such as proton transfer and proton-coupled electron transfer reactions. Herein, the real-time nuclear-electronic orbital time-dependent density functional theory (RT-NEO-TDDFT) approach is combined with a hybrid quantum mechanical/molecular mechanical (QM/MM) strategy to enable the accurate description of coupled nuclear-electronic quantum dynamics in the presence of heterogeneous environments such as solvent or proteins. The densities of the electrons and quantum protons are propagated in real time, while the other nuclei are propagated classically on the instantaneous electron-proton vibronic surface. This approach is applied to phenol bound to lysozyme, intramolecular proton transfer in malonaldehyde, and nonequilibrium excited-state intramolecular proton transfer in o-hydroxybenzaldehyde. These examples illustrate that the RT-NEO-TDDFT framework, coupled with an atomistic representation of the environment, allows the simulation of condensed-phase systems that exhibit significant nuclear quantum effects.

Dipole instability in molecules irradiated by XUV pulses

We study the response of small covalent molecules to XUV laser pulses. The theoretical description relies on a real-time and real-space Time-Dependent Density Functional Theory (TDDFT) approach at the level of the local density approximation complemented by an efficient self-interaction correction. We observe the development of a dipole instability well after the laser pulse has died out. We find that this instability mechanism is robust with respect to ionic motion, to a wide variety of laser characteristics and to the inclusion of incoherent correlations at the level of a relaxation time ansatz. To rule out any potential numerical effects, we use two independent computational implementations of the TDDFT approach. A comparison of the various laser parameters together with the widely used model approach consisting in an instantaneous hole excitation shows the generic character of this instability in terms of the level depletion of a deep lying electron state. An experimental verification of the phenomenon is proposed in terms of a time-resolved measurement of the photoelectron spectrum.