Time-dependent Density Functional Theory Results Research Articles

Time-dependent density-functional theory study on nonlocal electron stopping for inertial confinement fusion

Understanding laser–target coupling is of the utmost importance for achieving high performance in laser-direct-drive (LDD) inertial confinement fusion (ICF) experiments. Thus, accurate modeling of electron transport and deposition through ICF-relevant materials and conditions is necessary to quantify the total thermal conduction and ablation. The stopping range is a key transport quantity used in thermal conduction models; in this work, we review the overall role that the electron mean free path (MFP) plays in thermal conduction and hydrodynamic simulations. The currently used modified Lee–More model employs various physics approximations. We discuss a recent model that uses time-dependent density functional theory (TD-DFT) to eliminate these approximations in both the calculation of the electron stopping power and corresponding MFP in conduction zone polystyrene (CH) plasma. In general, the TD-DFT calculations showed a larger MFP (lower stopping power) than the standard modified Lee–More model. Using the TD-DFT results, an analytical model for the electron deposition range, λTD−DFT(ρ,T,K), was devised for CH plasmas between ρ=[0.05−1.05] g/cm3, kBT=[100−1000] eV. We implemented this model into LILAC, for simulations of a National Ignition Facility-scale LDD implosion and compared key physics quantities to ones obtained by simulations using the standard model. The implications of the obtained results and the path moving forward to calculate this same quantity in conduction-zone deuterium–tritium plasmas are further discussed, to hopefully close the understanding gap for laser target coupling in LDD-ICF simulations.

Error of relativistic effective core potentials for closed-shell diatomic molecules of p-block heavy and superheavy elements in DFT and TDDFT calculations.

Pseudopotentials (PP) are extensively used in electronic structure calculations, particularly for molecules containing heavy elements. Parameters in PPs are mainly determined from abinitio results, and errors of such PPs in density functional theory (DFT) calculations have been studied previously. However, PP errors on results with spin-orbit coupling and those in time-dependent DFT (TDDFT) calculations have not been reported previously. In this work, we investigate the error of the small-core energy-consistent Stuttgart/Koln pseudopotentials in DFT and TDDFT calculations with and without spin-orbit coupling. Ground state bond lengths, harmonic frequencies, dissociation energies, and vertical excitation energies for a series of closed-shell diatomic heavy and superheavy p-block molecules are calculated using several popular exchange-correlation functionals. PP errors are estimated by comparing with results using the all-electron Dirac-Coulomb (-Gaunt) Hamiltonian. Our results show that the difference between ground state properties and most excitation energies in scalar-relativistic calculations with the PP and those of all-electron calculations is quite small. This difference becomes somewhat larger when spin-orbit coupling (SOC) is present, especially for properties that are affected by SOC to some extent. In addition, the errors of the PPs are insensitive to the employed exchange-correlation functionals in most cases. Our results indicate that reasonable DFT and TDDFT results can be obtained using the small-core energy-consistent Stuttgart/Koln pseudopotentials for heavy and super-heavy p-block molecules.

Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion.

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light-matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.

On the Prediction of Spectroscopic Fingerprints of Co2+ Complexes Relevant for the ZIF Nucleation Process.

The nucleation process of zeolitic imidazolate frameworks (ZIFs) is to date not completely understood. Recently, it has been found that, during the formation of Co-ZIF-67, after mixing imidazole-type ligands with octahedral precursors containing oxygen-coordinated ligands, a metal-organic pool with a diversity of transition metal complexes (TMCs) is formed showing fingerprints of octahedral and tetrahedral Co2+ complexes with both types of ligands [Filez, M. Cell Rep. Phys. Sci. 2021, 2, 100680]. In order to further unravel this process, we aim to characterize the d-d transitions of the TMCs and focus on their number, intensity, and position, which change during the process and can thus serve as a fingerprint for the formed species. It was previously shown that the number of ligands and symmetry has a detrimental influence on the ground state properties of Co2+ TMCs. Herein, we investigate how far excited state properties of TMCs relevant during nanoporous formation processes can be predicted by time-dependent density functional theory (TDDFT) and ligand field density functional theory (LFDFT). As TMCs are known to be challenging systems with possibly degenerate ground states and double excitations, we first investigate the performance of both techniques on first-row octahedral aqua-complexes. With this knowledge, we then focus on tetrahedral Co2+ complexes with aqua and imidazole-type ligands in order to investigate in how far we can propose a spectroscopic fingerprint that allows us to follow the Co2+ complexes during the formation of Co-ZIF-67. The results of TDDFT and LFDFT are qualitatively in agreement and provide complementary information. We found that various features can be used to distinguish between the species. However, as LFDFT is not suited for TMCs possessing the extended imidazole-type ligands and double and spin-flip states are not included in TDDFT, both techniques need to be complemented with more advanced methods to obtain complete insight into the d-d excitations of TMCs with imidazole ligands. Therefore, we particularly explored ab initio ligand field theory, which is capable of describing double excitations and is, in contrast to LFDFT, suitable for TMCs with extended ligands.

Designing Efficient Metal-Free Dye-Sensitized Solar Cells: A Detailed Computational Study.

The modulation of molecular characteristics in metal-free organic dyes holds significant importance in dye-sensitized solar cells (DSSCs). The D-π-A molecular design, based on the furan moiety (π) in the conjugated spacer between the arylamine (D) and the 2-cyanoacrylic acid (A), was developed and theoretically evaluated for its potential application in DSSCs. Utilizing linear response time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional, different donor and acceptor groups were characterized in terms of the electronic absorption properties of these dyes. All the studied dye sensitizers demonstrate the ability to inject electrons into the semiconductor's conduction band (TiO2) and undergo regeneration through the redox potential triiodide/iodide (I3-/I-) electrode. TDDFT results indicate that the dyes with CSSH anchoring groups exhibit improved optoelectronic properties compared to other dyes. Further, the photophysical properties of all dyes absorbed on a Ti(OH)4 model were explored and reported. The observed results indicate that bidentate chemisorption occurs between dyes and TiO4H5. Furthermore, the HOMO-LUMO energy gaps for almost all dye complexes are significantly smaller than those of the free dyes. This decrease of the HOMO-LUMO energy gaps in the dye complexes facilitates electron excitation, and thus more photons can be adsorbed, guaranteeing larger values of efficiency and short-circuit current density.

Computational Screening of D-π-A Structured with Acceptor-Tuned Metal-Free Organic Dye Molecules for DSSCs

Four metal-free carbazole-based acceptor-tuned organic molecules (denoted as CBa1–CBa4) based on electron-donor, [Formula: see text]-spacer and electron-acceptor (D-[Formula: see text]-A) for dye-sensitized solar cells (DSSCs) have been newly designed. The electronic structures, optical absorption ultraviolet-visible (UV–Vis) properties and photovoltaic (PV) parameters of CBa1–CBa4 dyes were computationally studied by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. These molecules were planned through chemical alterations of the acceptor group of a literature-based organic dye known as CB1 dye. The planning of CBa1–CBa4 dyes was to decrease the highest occupied molecular orbitals (HOMOs) and lowest unoccupied MOs (LUMOs) of the energy gap ([Formula: see text]) and to red-shift their UV–Vis response compared to CB1. This study was initially performed using the exchange correctional (XC) and long-range corrected (LC) with the computational ideal in the TD-DFT method significantly to get an accurate absorption wavelength for CB1. From the XC and LC results, CAM-B3LYP functional is better matched with CB1. So, further newly organic CBa1–CBa4 dyes UV–Vis spectra were followed by this method. According to DFT and TDDFT results, CBa1 and CBa2 molecules were found to have reduced HOMOs–LUMOs energy gap, longer UV–Vis spectra and faster charger transfer (CT) character compared to CB1. The conclusion recommends that the newly designed molecules are hopeful and appropriate for optoelectronic devices. Hence, the work predicts to support the new scheming carbazole-based molecules with the studied properties for synthetizing to DSSC applications.

Experimental and theoretical evaluation of N-pyridoxal-salicylic acid hydrazide derived copper(II) complex with 2-methylimidazole

This article deals with the experimental and theoretical evaluations of N-pyridoxal-salicylic acid hydrazide (H2pd-sah) 1 and its mixed-ligand copper(II) complex with 2-methylimidazole, [Cu(pd-sah)(MeImdH)] 2. The compounds were characterized based on spectral (UV/Vis. IR) methods, powder-XRD, elemental analysis, and molar conductivity measurements. Both compounds' molecular structure and charge analysis were computed through B3LYP with 6-311 G (d, p) and LANL2DZ basic set using the Gaussian 09 W program package. The time-dependent density functional theory (TD-DFT) approach is used in gas-phase electronic transitions of 2 using the LANL2DZ basis set. Also, the computed UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones. The molecular structure based on theoretical investigation reveals that compound 2 adopts a distorted square planer N2O2 coordination sphere around the Cu(II). The ONO donor atoms of hydrazone moiety and one nitrogen of 2-methylimidazole constitute the N2O2 basal plane. Moreover, the in-vitro antioxidant activity was evaluated by DPPH assay in both compounds. In addition, Molecular docking studies were performed to predict the binding interaction between compound 2 and the Human Serum Albumin HSA (PDB ID: 1H9Z). Communicated by Ramaswamy H. Sarma

WITHDRAWN: Utility of Warped C80H30 nanographene for removal of toxic heavy metal ions from wastewater

The removal of heavy metal ions from wastewater has been a global issue as such ions pose significant health and environmental impacts. Drawing on a nanographene (NG), the present study employs density functional theory (DFT) to evaluate an effective heavy metal removal method for the purpose of removing Pb 2+ , Hg 2+ , and Cd 2+ ions from wastewater. NG was found to have high effectiveness and efficiency in capturing the heavy metals of aqueous media. Furthermore, the adsorption of Pb 2+ , Hg 2+ , and Cd 2+ ions was found to have the capability of diminishing the significant pristine NG (HOMO-LUMO) gap. The findings showed larger cation-NG charge transfers and greater binding energy in cation-NG systems that have larger transport rates of electrons. According to the time-dependent DFT results, the complexes under study were found to have “ligand-to-metal charge transfer” excitations. As a result, the theoretical findings of the present work could contribute to experimental works on identifying NG-based efficient and effective substances for the removal of contaminants from wastewater. • The first DFT study on the adsorption of pollutant Cd 2+ , Hg 2+ , and Pb 2+ ions on NG layer. • Detailed analysis of possible charge transfers between the cations and the NG. • TD-DFT analysis showed “ligand to metal charge transfer” excitations for the complexes.

Unprecedented platinum(II) coordination compound of sterically hindered 3,3′-bis(NH-benzimidazol-2-yl)-2,2′-bipyridine ligand

The synthesis, spectroscopic characterization, single-crystal X-ray diffraction (SCXD) analysis, and Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) studies of the coordination compound of cis-dichloroplatinum(II) with a sterically hindered N4-donor ligand, 3,3′-bis(NH-benzimidazol-2-yl)-2,2′-bipyridine (L), [Pt(L)Cl2]⋅DMSO (1) (DMSO = dimethyl sulfoxide) are reported. The Pt(II) ion adopts a slightly distorted square-planar geometry in which L coordinates in a bidentate fashion to the metal center through N atom of benzimidazole (bim) and N atom of pyridine (py) to form a seven-membered ring. The molecular units in the lattice are held together in a head to tail fashion as a dimer through intermolecular hydrogen bonding between the uncoordinated bim and py rings in the molecule through N H⋅⋅⋅N hydrogen bonds with the R22 (14) graph-set motif. The lattice DMSO solvent molecule significantly stabilizes the structure through N H⋅⋅⋅O hydrogen bond with the coordinated bim in the structure. Hirshfeld surface analysis also confirmed the hydrogen bond interactions in the crystal. DFT and TD-DFT results show that optimized geometry and UV-vis absorption spectra are consistent with the experimental results. Natural bond orbital (NBO) properties show that the hydrogen bond stability between the two monomers attributes with large stabilization energy values.

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Molecular structure, intramolecular hydrogen bond strength, vibrational assignment, and spectroscopic insight of 4-phenylamino-3-penten-2-one and its derivatives: A theoretical and experimental study

A number of phenyl-substituted derivatives of 4-phenylamino-pent-3-en-2-one, APO-NPh, were synthesized. Their structures, intramolecular hydrogen bond strength, vibrational assignment, fluorescence, NMR, and UV spectra were studied by the help of density functional theory (DFT) and time-dependent density functional theory(TD-DFT) calculations, at the B3LYP/6-311++G** level, and also experimental techniques. The 2-fluoro, and 2,6-dimethyl derivatives showed reduced intramolecular hydrogen bond strength, while the 4-nitro, 4-ethyl ester increased it and 3-chloro and 3-bromo showed no change in comparison to APO-NPh. For the assignment of IR and Raman spectra of APO-NPh, isotope effects, GaussView animation, and potential energy distributions (PED) contributions were used. Also, for the best assignment, the 4-amino-3-penten-2-one (APO) and their VEDA's PED contributions were compared. Since in the titled molecules the NH stretching are covered by the aliphatic and aromatic CH stretching motions, the NH stretching frequencies were estimated using experimental ND stretching frequencies. The estimated frequencies are in good agreement with other theoretical and experimental results for intramolecular hydrogen bond strength. According to the frequency shifts upon deuteration for APO and APO-NPh, the assignment by the GaussView animation and VEDA's PED contributions show no important difference, except for the NH rocking, which appeared at 1320 cm−1. The theoretical results predicted two conformers for the ortho and meta substituted compounds. The X-ray result for the 2-fluoro derivative (3) shows that the major form is the one with fluorine closest to NH. TD-DFT and fluorescence results confirmed that aminoketone, iminoketone tautomerism is likely in the first excited state.

Theoretical Investigation of S, P, and O-Doping Effect on the Photocatalytic Efficiency of g-C3-N4 Monolayer

Graphitic carbon nitride (g-C 3 N 4 ) is a low-cost photocatalyst with high stability and many applications. However, photocatalytic activity of g-C 3 N 4 has been limited due to its low visible light absorption and high electron-hole pair recombination rate. In this study, the effect of P and O doping on the geometrical and electronic properties of the g-C 3 N 4 is investigated using density functional theory (DFT) calculations. The results showed that the surface area increased in the cases of the S- and P-doped systems. Electron density distribution of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular (LUMO), and natural bond orbital (NBO) analyses illustrated that, among the S- and O-doped systems, S int - and O int -doped g-C 3 N 4 structures had high delocalization. Delocalization of electrons increased after non-metal doping at the edge site. Phosphorus doping at the N edge site led to a stronger donor-acceptor interaction. The most stable configuration was related to doping at the edge (S- and O-doped) and corner carbon (P-doped) site. According to the results of Time-dependent density-functional theory (TD-DFT) calculations, the S ed - and P C -doped g-C 3 N 4 had more light harvesting ability and less overlap integral than g-C 3 N 4 quantum dots (QCNs) and O ed -doped CN had more light harvesting ability than QCNs. On the basis of the results, non-metal doping increased visible light-harvesting and lifetime of the e - -h + pair, which led to increased photocatalytic efficiency.

Theoretical study of the absolute inner-shell photoionization cross sections of the formic acid and some of its hydrogen-bonded clusters.

Inner-shell absolute photoabsorption and photoionization cross sections of the formic acid, HCOOH, and its small hydrogen-bonded clusters, i.e., (HCOOH)2, HCOOH2 +, HCOHOH+, and HCOOH·H3O+, were calculated at the time-dependent density functional theory (TDDFT) level, and the results were used to analyze the effect of the formic acid clustering on the carbon and oxygen K-edge photoionization cross sections. The discrete electronic pseudospectra obtained with square-integrable (L2) basis set calculations were used in an analytic continuation procedure based on continued fraction functions to obtain the photoabsorption cross sections. Symmetry adapted cluster configuration interaction calculations on the small formic acid clusters have also been performed at the oxygen K-edge to assign the discrete transitions and ionization potentials in support to the TDDFT results.

Surface Hopping within an Exciton Picture. An Electrostatic Embedding Scheme.

We report the development and the implementation of an exciton approach that allows ab initio nonadiabatic dynamics simulations of electronic excitation energy transfer in multichromophoric systems. For the dynamics, a trajectory-based strategy is used within the surface hopping formulation. The approach features a consistent hybrid formulation that allows the construction of potential energy surfaces and gradients by combining quantum mechanics and molecular mechanics within an electrostatic embedding scheme. As an application, the study of a molecular dyad consisting of a covalently bound BODIPY moiety and a tetrathiophene group is presented using time-dependent density functional theory (TDDFT). The results obtained with the exciton model are compared to previously performed full TDDFT dynamics of the same system. Our results show excellent agreement with the full TDDFT results, indicating that the couplings that lead to excitation energy transfer (EET) are dominated by Coulomb interaction terms and that charge-transfer states are not necessary to properly describe the nonadiabatic dynamics of the system. The exciton model also reveals ultrafast coherent oscillations of the excitation between the two units in the dyad, which occur during the first 50 fs.

Assessment of Ab Initio and Density Functional Theory Methods for the Excitations of Donor-Acceptor Complexes: The Case of the Benzene-Tetracyanoethylene Model.

The understanding of the excited-state properties of electron donors, acceptors and their interfaces in organic optoelectronic devices is a fundamental issue for their performance optimization. In order to obtain a balanced description of the different excitation types for electron-donor-acceptor systems, including the singlet charge transfer (CT), local excitations, and triplet excited states, several ab initio and density functional theory (DFT) methods for excited-state calculations were evaluated based upon the selected model system of benzene-tetracyanoethylene (B-TCNE) complexes. On the basis of benchmark calculations of the equation-of-motion coupled-cluster with single and double excitations method, the arithmetic mean of the absolute errors and standard errors of the electronic excitation energies for the different computational methods suggest that the M11 functional in DFT is superior to the other tested DFT functionals, and time-dependent DFT (TDDFT) with the Tamm–Dancoff approximation improves the accuracy of the calculated excitation energies relative to that of the full TDDFT. The performance of the M11 functional underlines the importance of kinetic energy density, spin-density gradient, and range separation in the development of novel DFT functionals. According to the TDDFT results, the performances of the different TDDFT methods on the CT properties of the B-TCNE complexes were also analyzed.

Accuracy of Td-DFT in the Ultraviolet and Circular Dichroism Spectra of Deoxyguanosine and Uridine.

Accuracy of the time-dependent density functional theory (Td-DFT) was examined for the ultraviolet (UV) and circular dichroism (CD) spectra of deoxyguanosine (dG) and uridine, using 11 different DFT functionals and two different basis sets. The Td-DFT results of the UV and CD spectra were strongly dependent on the functionals used. The basis-set dependence was observed only for the CD spectral calculations. For the UV spectra, the B3LYP and PBE0 functionals gave relatively good results. For the CD spectra, the B3LYP and PBE0 with 6-311G(d,p) basis gave relatively permissible result only for dG. The results of other functionals were difficult to be used for the studies of the UV and CD spectra, though the symmetry adapted cluster-configuration interaction (SAC-CI) method reproduced well the experimental spectra of these molecules. To obtain valuable information from the theoretical calculations of the UV and CD spectra, the theoretical tool must be able to reproduce correctly both of the intensities and peak positions of the UV and CD spectra. Then, we can analyze the reasons of the changes of the intensity and/or the peak position to clarify the chemistry involved. It is difficult to recommend Td-DFT as such tools of science, at least from the examinations using dG and uridine.

TDDFT calculations and photoacoustic spectroscopy experiments used to identify phenolic acid functional biomolecules in Brazilian tropical fruits in natura

Time-dependent density functional theory (TDDFT) calculations of electronic transitions have been widely used to determine molecular structures. The excitation wavelengths and oscillator strengths obtained with the hybrid exchange-correlation functional B3LYP in conjunction with the ADZP basis set are employed to simulate the UV–Vis spectra of eight phenolic acids. Experimental and theoretical UV–Vis spectra reported previously in the literature are compared with our results. The fast, sensitive and non-destructive technique of photoacoustic spectroscopy (PAS) is used to determine the UV–Vis spectra of four Brazilian tropical fresh fruits in natura. Then, the PAS along with the TDDFT results are for the first time used to investigate and identify the presence of phenolic acids in the fruits studied in this work. This theoretical method with this experimental technique show to be a powerful and cheap tool to detect the existence of phenolic acids in fruits, vegetables, cereals, and grains. Comparison with high performance liquid chromatography results, when available, is also carried out.

Efficient enhancement of second order nonlinear optical response by complexing metal cations in conjugated 7-substituted coumarin

Most of the coumarins have been found useful as non-linear optical chromophores. The four novel water-soluble coumarin-based compounds (OC6, NC6, OC7, and NC7) and the metallic compounds of NC7 with different metal cations (Na+, K+, Mg2+, Ca2+, Fe2+, and Zn2+) have been investigated by carrying out density functional theory (DFT). Our DFT calculations revealed that the second-order nonlinear optical properties have a pronounced enhancement by means of the introduction of π-conjugatd electron donor (dimethylamino phenyl alkynyl) in 7-position of the coumarin ring and metal cations, especially for transition metals. The further investigations of the larger first hyperpolarizability (βtot) reveal that the NC7*Fe2+ and NC7*Zn2+ present the larger values as 1.151 × 10−27 and 1.083 × 10−27 esu owing to the lower transition energies and larger oscillator strengths of crucial electronic transitions. Moreover, time-dependent DFT results show that the large intramolecular charge transfers exist in the NC7*Fe2+ and NC7*Zn2+. In addition, the natural bond orbital analysis demonstrated that the second-order stabilization energies is from the lone pair (LP) orbital on O atom to the LP* orbital of metal cations interaction correlate with the O-Mn+ atomics distance. On the other hand, the atoms in molecules analysis showed that the O-Mn+ interactions can be characterized by the presence of a bond critical point (BCP) and the O-Fe2+ and O-Zn2+ interactions have partially ionic and partially covalent bonds rather than an electrostatic character for O-Mn+ (Na+, K+, Mg2+ and Ca2+). In addition, the delocalization indices of O-Mn+ bonds correlate reasonably well with electron density, kinetic and potential energy densities in these complexes. Thus, we hope this research will introduce a new relation between the structure and the property of chromophore nonlinear optical activity.

Change in optoelectronic properties of ExBox+4 on functionalization and guest encapsulation.

The impact of functionalization as well as guest encapsulation on the optoelectronic properties of the ExBox+4 moiety has been investigated with the aid of density functional theory (DFT) based calculations. To this end, three functionalized variants of the ExBox+4 moiety have been modelled in silico, viz. NH2-ExBox+4-F, CN-ExBox+4-NH2 and NO2-ExBox+4-NH2, whereas coronene (Cor), B-doped coronene (BCor), N-doped coronene (NCor), tetrathiafulvalene (TTF), biphenyl (BiPh), tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) molecules have been employed as guests. The results indicate that as a result of functionalization, the ExBox+4 moiety can exhibit tangible non-linear optical (NLO) response properties as vindicated by the first static hyperpolarizability (β). As a result of guest encapsulation, significant variation in the optoelectronic properties of the chosen hosts takes place. BCor/TCNQ/NCor molecules enhance the NLO activity of the hosts while TTF/TCNE suppresses the same. In particular, NCor@host moieties demonstrate very high β values at the static field limit. Time dependent DFT results suggest that in general, the ability of the guest in tuning the transition energy associated with the pivotal electronic transitions of the host plays the dominant role in the observed variation in β. In addition, BCor/NCor@host moieties demonstrate broadband optical absorption capability thereby elucidating the possibility of deriving multi-purpose optoelectronic features such as NLO activity as well as utility in photovoltaic systems. Thermochemical results suggest that all the guest@host systems are stable at 298.15 K. Non-covalent and electrostatic binding forces stabilize the studied systems.

Electronic Absorption Spectra of Tetrapyrrole-Based Pigments via TD-DFT: A Reduced Orbital Space Study.

Tetrapyrrole-based pigments play a crucial role in photosynthesis as principal light absorbers in light-harvesting chemical systems. As such, accurate theoretical descriptions of the electronic absorption spectra of these pigments will aid in the proper description and understanding of the overall photophysics of photosynthesis. In this work, time-dependent density functional theory (TD-DFT) at the CAM-B3LYP/6-31G* level of theory is employed to produce the theoretical absorption spectra of several tetrapyrrole-based pigments. However, the application of TD-DFT to large systems with several hundreds of atoms can become computationally prohibitive. Therefore, in this study, TD-DFT calculations with reduced orbital spaces (ROSs) that exclude portions of occupied and virtual orbitals are pursued as a viable, computationally cost-effective alternative to conventional TD-DFT calculations. The effects of reducing orbital space size on theoretical spectra are qualitatively and quantitatively described, and both conventional and ROS results are benchmarked against experimental absorption spectra of various tetrapyrrole-based pigments. The orbital reduction approach is also applied to a large natural pigment assembly that comprises the principal light-absorbing component of the reaction center in purple bacteria. Overall, we find that TD-DFT calculations with proper and judicious orbital space reductions can adequately reproduce conventional, full orbital space, TD-DFT results of all pigments studied in this work.