Toward Accurate Two-Photon Absorption Spectrum Simulations: Exploring the Landscape beyond the Generalized Gradient Approximation.

In this Letter, we present a pioneering analysis of the density functional approximations (DFAs) beyond the generalized gradient approximation (GGA) for predicting two-photon absorption (2PA) strengths of a set of push-pull π-conjugated molecules. In more detail, we have employed a variety of meta-generalized gradient approximation (meta-GGA) functionals, including SCAN, MN15, and M06-2X, to assess their accuracy in describing the 2PA properties of a chosen set of 48 organic molecules. Analytic quadratic response theory is employed for these functionals, and their performance is compared against the previously studied DFAs and reference data obtained at the coupled-cluster CC2 level combined with the resolution-of-identity approximation (RI-CC2).

Radiation-Driven Polymerisation of Methacrylic Acid in Aqueous Solution: A Chemical Events Monte Carlo Study.

This study employed a coarse-grained Monte Carlo (MC) simulation to investigate the radiation-induced polymerisation of methacrylic acid (MAA) in an aqueous solution. This method provides an alternative to traditional kinetic models, enabling a detailed examination of the micro-structure and growth patterns of MAA polymers, which are often not captured in other approaches. In this work, we generated multiple clones of a simulation box, each containing a specific chemical composition.

A polarizable coarse-grained model for metal, metal oxide and composite metal/metal oxide nanoparticles: development and implementation.

We present a polarizable coarse-grained model for metal, metal oxide, and composite metal/metal oxide nanoparticles with well-defined crystalline surfaces. The developed model uses a low-resolution polarizable "surface beads" representation of the nanoparticle's geometry and pairwise cross nanoparticle potential consisting of van der Waals and electrostatic interaction terms. The electrostatic interaction term of the cross nanoparticle potential incorporates a crucial physical aspect of electrostatic interaction into the metal and metal oxide systems, such as induced surface charges, making it possible to explore the nanoparticles' behavior in complex environments as well as investigate the interplay between electrostatic and van der Waals interactions in nanoparticle systems.

A polarizable coarse-grained model for metal, metal oxide and composite metal/metal oxide nanoparticles and its applications.

We present a selected set of exemplifying applications of the novel polarizable coarse-grained model [see the first part] to various outstanding problems in the physics and chemistry of nanoparticles: electrostatic potential around silver and gold nanoparticles; spontaneous and external electric field-driven self-organization of gold and silver nanoparticle systems; and physisorption of carbon dioxide on titanium dioxide nanoparticles decorated with a gold catalyst. In the first application, the developed model has shown capabilities of predicting long-range potential with accuracy comparable to the tight-binding density functional theory methods. Furthermore, the electrostatic potential analysis in hot spot regions allowed us to identify twin defect lines in a silver nanostar as a promising candidate for an enhancer in surface-enhanced Raman spectroscopy.

Antibacterial Activity of Silver and Gold Particles Formed on Titania Thin Films.

Metal-based nanoparticles with antimicrobial activity are gaining a lot of attention in recent years due to the increased antibiotics resistance. The development and the pathogenesis of oral diseases are usually associated with the formation of bacteria biofilms on the surfaces; therefore, it is crucial to investigate the materials and their properties that would reduce bacterial attachment and biofilm formation. This work provides a systematic investigation of the physical-chemical properties and the antibacterial activity of TiO thin films decorated by Ag and Au nanoparticles (NP) against and species associated with oral diseases.

Electronic -Tensor Calculations for Dangling Bonds in Nanodiamonds.

The electronic -tensor calculations are performed for dangling bonds (DBs) introduced into nanodiamonds (NDs) with four different functional groups on their surfaces. For hydrogenated and fluorinated NDs, it is found that -shifts of the latter vary in a much wider range, and the same is also true for the total energy differences between the highest and the lowest energy DBs. In addition, it is shown that the shape of NDs significantly impacts the energetics and -shifts of DBs, whereas the influence of the size is much less pronounced, as is the influence of the presence of one DB in the vicinity of the other, resulting in no substantial change on their magnetic behavior.

Size-dependent polarizabilities and van der Waals dispersion coefficients of fullerenes from large-scale complex polarization propagator calculations.

While the anomalous non-additive size-dependencies of static dipole polarizabilities and van der Waals C dispersion coefficients of carbon fullerenes are well established, the widespread reported scalings for the latter (ranging from N to N) call for a comprehensive first-principles investigation. With a highly efficient implementation of the linear complex polarization propagator, we have performed Hartree-Fock and Kohn-Sham density functional theory calculations of the frequency-dependent polarizabilities for fullerenes consisting of up to 540 carbon atoms. Our results for the static polarizabilities and C coefficients show scalings of N and N, respectively, thereby deviating significantly from the previously reported values obtained with the use of semi-classical/empirical methods.

Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the self-consistent field approximation.

Within the self-consistent field approximation, computationally tractable expressions for the isotropic second-order hyperpolarizability have been derived and implemented for the calculation of two-photon absorption cross sections. The novel tensor average formulation presented in this work allows for the evaluation of isotropic damped cubic response functions using only ∼3.3% (one-photon off-resonance regions) and ∼10% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components.

Plasmonic nano-shells: atomistic discrete interaction versus classic electrodynamics models.

Using the extended discrete interaction model and Mie theory, we investigate the tunability of the optical polarizability of small metallic nano-shells. We show that the spectral positions of symmetric and antisymmetric dipolar plasmon resonances vary with the ratio of particle radius to hole radius in a manner similar to one predicted for uniform metallic nano-shells using a semiclassical approach of two coupled harmonic oscillators. We show that, according to the extended discrete interaction model, the dipolar plasmon resonances are also present for nano-shells in the 2-13 nm size region and show the same functional dependence seen for larger nano-shells.

Dalton Project: A Python platform for molecular- and electronic-structure simulations of complex systems.

The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex molecular environments. The platform is written in Python and defines a means for library communication and interaction. Intermediate data such as integrals are exposed to the platform and made accessible to the user in the form of NumPy arrays, and the resulting data are extracted, analyzed, and visualized.

Computational study on the electronic g-tensors of hydrophilic and hydrophobic nanodiamonds interacting with water.

Hydrogenated and hydroxylated nanodiamonds (NDs) are modeled by putting emphasis on the most common paramagnetic impurities-dangling bonds as well as single substitutional nitrogen atoms-and their interaction with water. It is shown that, despite its overall hydrophobicity, hydrogenated ND can become locally hydrophilic due to the introduced defects; therefore, water molecules may be attracted to the particular sites at its surface. To assess the direct influence of water on the magnetic behavior of NDs, the solvent-induced shift of the g-tensor was employed, indicating that for the same types of impurities, the impact the water has strongly depends on their positions in ND.

Electronic g-tensors of nanodiamonds: Dependence on the size, shape, and surface functionalization.

The electronic g-tensor dependence on the size, shape, and surface functionalization of nanodiamonds (NDs) is theoretically investigated by selecting dangling bonds and single substitutional nitrogen atoms as a main source of the unpaired electrons. The performed g-tensor calculations reveal that aforementioned paramagnetic impurities introduced into octahedrally shaped ND of CH size behave in a very similar manner as those embedded into a smaller octahedral model of CH size. Since cubic and tetrahedral NDs-CH and CH-demonstrate a wider range of g-shift values than octahedral systems, the g-tensor dependence on different shapes can be considered as more pronounced.

Optomagnetic Effect Induced by Magnetized Nanocavity Plasmon.

We propose a new type of optomagnetic effect induced by a highly confined plasmonic field in a nanocavity. It is shown that a very large dynamic magnetic field can be generated as the result of the inhomogeneity of nanocavity plasmons, which can directly activate spin-forbidden transitions in molecules. The dynamic optomagnetic effects on optical transitions between states of different spin multiplicities are illustrated by first-principles calculations for C.

On the magnetic properties of nanodiamonds: Electronic g-tensor calculations.

The electronic g-tensor calculations are carried out for various paramagnetic defects introduced into hydrogenated diamond nanocrystal CH, showing that such a system can be successfully used to model magnetic properties of nanodiamonds (NDs) with paramagnetic centers containing no vacancies. In addition, it is revealed that, depending on the geometric positions in ND, paramagnetic centers of the same type produce noticeable variations of the g-tensor values. A side-by-side comparison of the performance of effective nuclear charge and spin-orbit mean field (SOMF) approaches indicates that the latter is more sensitive to the quality of basis sets, especially concerning diffuse functions, the inclusion of which is found to be nonbeneficial.

Mechanistic Studies on NaHCO Hydrogenation and HCOOH Dehydrogenation Reactions Catalysed by a Fe Linear Tetraphosphine Complex.

We present a theoretical extension of the previously published bicarbonate hydrogenation to formate and formic acid dehydrogenation catalysed by Fe complexes bearing the linear tetraphosphine ligand tetraphos-1. The hydrogenation reaction was found to proceed at the singlet surface with two competing pathways: A) H association to the Fe-H species followed by deprotonation to give a Fe(H) intermediate, which then reacts with CO to give formate. B) CO insertion into the Fe-H bond, followed by H association and subsequent deprotonation.

Formation of N-oxide in the third oxidation of [Ru(tpy)(L)(OH)].

The widely studied water oxidation catalyst [Ru(tpy)(L)(OH)] (tpy = 2,2':6',2''-terpyridine, L = bpy = 2,2'-bipyridine or L = bpm = 2,2'-bipyrimidine) is still under scrutiny. Here we present a new suggestion for one of the key steps, results that could resolve conflicting interpretations of experimental results. Instead of the previously proposed Ru[double bond, length as m-dash]O species, a proposed key species in water oxidation catalysis, we propose that the third oxidation of Ru could lead to a RuN-oxide, via rapid water coordination followed by oxidation and concerted N-O bond formation.

Origin of the Absorption Band of Bromophenol Blue in Acidic and Basic pH: Insight from a Combined Molecular Dynamics and TD-DFT/MM Study.

We study the linear and nonlinear optical properties of a well-known acid-base indicator, bromophenol blue (BPB), in aqueous solution by employing static and integrated approaches. In the static approach, optical properties have been calculated using time-dependent density functional theory (TD-DFT) on the fully relaxed geometries of the neutral and different unprotonated forms of BPB. Moreover, both closed and open forms of BPB were considered.

Quantum mechanics capacitance molecular mechanics modeling of core-electron binding energies of methanol and methyl nitrite on Ag(111) surface.

We study a newly devised quantum mechanics capacitance molecular mechanics (QMCMM) method for the calculation of core-electron binding energies in the case of molecules adsorbed on metal surfaces. This yet untested methodology is applied to systems with monolayer of methanol/methyl nitrite on an Ag(111) surface at 100 K temperature. It was found out that the studied C, N, and O 1s core-hole energies converge very slowly as a function of the radius of the metallic cluster, which was ascribed to build up of positive charge on the edge of the Ag slab.

Optical Properties of Gold Nanoclusters Functionalized with a Small Organic Compound: Modeling by an Integrated Quantum-Classical Approach.

Motivated by the growing importance of organometallic nanostructured materials and nanoparticles as microscopic devices for diagnostic and sensing applications, and by the recent considerable development in the simulation of such materials, we here choose a prototype system - para-nitroaniline (pNA) on gold nanoparticles - to demonstrate effective strategies for designing metal nanoparticles with organic conjugates from fundamental principles. We investigated the motion, adsorption mode, and physical chemistry properties of gold-pNA particles, increasing in size, through classical molecular dynamics (MD) simulations in connection with quantum chemistry (QC) calculations. We apply the quantum mechanics-capacitance molecular mechanics method [Z.

Hybrid Complex Polarization Propagator/Molecular Mechanics Method for Heterogeneous Environments.

We introduce a hybrid complex polarization propagator/molecular mechanics method for the calculation of near-resonant and resonant response properties of molecules in heterogeneous environments, which consist of a metallic surface, or nanoparticle, and a solvent. The applicability and performance of the method is demonstrated by computations of linear absorption spectra of p-nitroaniline physisorbed at a gold/dimethyl sulfoxide interface in the UV/vis and near-carbon-K-edge regions of the spectrum. It is shown that the shift of absorption cross-section induced by the heterogeneous environment varies significantly depending on the nature of the excited states encountered in the targeted frequency region as well as on the actual size of the resonant frequencies, and that the solvent component of the heterogeneous environment is responsible for the major part of the environmental shift, especially in the higher frequency range of the carbon K-edge region.

Two-Photon Absorption of Metal-Assisted Chromophores.

Aiming to understand the effect of a metal surface on nonlinear optical properties and the combined effects of surface and solvent environments on such properties, we present a multiscale response theory study, integrated with dynamics of the two-photon absorption of 4-nitro-4'-amino-trans-stilbene physisorbed on noble metal surfaces, considering two such surfaces, Ag(111) and Au(111), and two solvents, cyclohexane and water, as cases for demonstration. A few conclusions of general character could be drawn: While the geometrical change of the chromophore induced by the environment was found to notably alter (diminish) the two-photon absorption cross section in the polar medium, the effects of the metal surface and solvent on the electronic structure of the chromophore surpasses the geometrical effects and leads to a considerably enhanced two-photon absorption cross section in the polar solvent. This enhancement of two-photon absorption arises essentially from the metal charge image induced enlargement of the difference between the dipole moment of the excited state and the ground state.

Toward fully nonempirical simulations of optical band shapes of molecules in solution: a case study of heterocyclic ketoimine difluoroborates.

This study demonstrates that a hybrid density functional theory/molecular mechanics approach can be successfully combined with time-dependent wavepacket approach to predict the shape of optical bands for molecules in solutions, including vibrational fine structure. A key step in this treatment is the estimation of the inhomogeneous broadening based on the hybrid approach, where the polarization between solute and atomically decomposed solvent is taken into account in a self-consistent manner. The potential of this approach is shown by predicting optical absorption bands for three heterocyclic ketoimine difluoroborates in solution.

Quantum mechanics/molecular mechanics modeling of photoelectron spectra: the carbon 1s core-electron binding energies of ethanol-water solutions.

Using ethanol-water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute-solvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics model-electrostatic, polarization, and van der Waals-with atom or bond granulation of the corresponding MM charge and polarizability force-fields.

A time-dependent density-functional theory and complete active space self-consistent field method study of vibronic absorption and emission spectra of coumarin.

Time-dependent density-functional theory (TD-DFT) and complete active space multiconfiguration self-consistent field (CASSCF) calculations have been used to determine equilibrium structures and vibrational frequencies of the ground state and several singlet low-lying excited states of coumarin. Vertical and adiabatic transition energies of S1, S2, and S3 have been estimated by TD-B3LYP and CASSCF/PT2. Calculations predict that the dipole-allowed S1 and S3 states have a character of (1)(ππ*), while the dipole-forbidden (1)(nπ*) state is responsible for S2.