A new method to analyze and understand molecular linear and nonlinear optical responses via field-induced functions: a straightforward alternative to sum-over-states (SOS) analysis

The sum-over-states (SOS) method allows the computation of polarizabilities and hyperpolarizabilities additively from the contributions of different electronic excited states in a given molecule or cluster. Subsequent analysis of the main excited configurations contributing to the relevant excited states allows characterizing the orbitals involved in the linear and nonlinear optical response. Unfortunately, the chemically relevant information that can be obtained by SOS is hindered by a series of methodological and computational drawbacks. Among these drawbacks, we can highlight the high computational cost, problems arising from nonconvergent series and errors caused by the inaccurate description of excitation energies and/or higher excited state matrix elements. For this reason, coupled-perturbed schemes are currently widely used to determine the NLO potential of molecules and materials. However, such a choice limits the amount of intuitive chemical information that, on the other hand, can be retrieved by a successful SOS computation. In this work, we present and discuss a novel computational strategy that offers the means to extract the useful chemical insights from a coupled-perturbed calculation at almost negligible extra computational cost providing a transparent picture about orbital contributions to the properties of interest. The proposed method is based on the generation and further analysis of field-induced orbitals, FIOs, from the analytic or numerical derivatives of the dipole moment. Orbital symmetry rules are derived using group theory and the method is tested for a series of small and medium size systems.Xunta de Galicia | Ref. GRC2015/01

On the shape dependence of cluster (hyper)polarizabilities. A combined ab initio and DFT study on large fullerene-like gallium arsenide semiconductor clusters

cited By 11International audienceThe effect of the cluster shape on the magnitudes of the static dipole (hyper)polarizabilities of large gallium arsenic clusters built from 72 atoms is presented and discussed. Also, the performance of conventional and long range corrected density functionals is assessed on the prediction of the static electric dipole hyperpolarizabilities. The reported results obtained at the Hartree-Fock, (LC-) BLYP, (LC-) BPW91, (CAM)-B3LYP, and WB97XD levels of theory demonstrate that the cluster shape not only dominates the magnitude of the second hyperpolarizabilities of clusters but also affects dramatically the performance of the density functional theory functionals used. Copyright © 2010 Wiley Periodicals, Inc

How large are the microscopic electronic dipole (hyper)polarizabilities of CdnTen bare clusters compared to those of CdnSn and CdnSen? A systematic ab initio study

cited By 15International audienceThe static mean dipole polarizabilities, the polarizability anisotropies and the second hyperpolarizabilities of the ground state structures of stoichiometric CdnTen (n = 2, 3, 4, 5, 9) clusters are presented for the first time and they are compared with those of selected CdnSn and CdnSen clusters. Our ab initio results suggest that the CdTe clusters are significantly more hyperpolarizable than clusters constituted by CdS, and CdSe, in accordance to earlier experimental measurements. Also, it is demonstrated that the second hyperpolarizability magnitudes computed at different theoretical equilibrium geometries of the same cluster, determined by geometry optimization at different levels of theory, are significantly sensitive to the obtained equilibrium inter-atomic distances among the electropositive Cd atoms. © 2009 Elsevier B.V. All rights reserved

Second-hyperpolarizability (γ) enhancement in metal-decorated zigzag graphene flakes and ribbons: The size effect

cited By 20International audienceA study about the size-dependence of the hyperpolarizability-enhancement observed in metal-functionalized finite graphene species is presented. The reported ab initio and density functional results suggest that edge-passivation of graphene fragments with metallic agents (in this case Li) triggers an impressive enhancement of the second hyperpolarizability at the static limit. However, such a trend holds only in small graphene-type fragments. Strong evidence is provided showing that the specific effect drastically weakens with increasing the size of the graphene fragments regardless of their shape. The observed hyperpolarizability-enhancement in small systems and its severe decrease with increasing the size of the graphene species is qualitatively explained in terms of their charge transfer polarization mechanism. © 2013 American Chemical Society

Comment on "How the number and location of lithium atoms affect the first hyperpolarizability of graphene"

cited By 2International audienceno abstrac

Fullerene-C 60 in contact with alkali metal clusters: Prototype nano-objects of enhanced first hyperpolarizabilities

cited By 43International audienceThe electric first hyperpolarizabilities (β) of a representative set of alkali metal droplets in contact with fullerene (C 60) have been explored at the static limit via ab initio and density functional theory methods for the first time. We find that, when alkali metal droplets are adsorbed on the surface of C 60, systems of enhanced static dipolar and/or octupolar hyperpolarizabilities are delivered. Both the type and the magnitudes of the first hyperpolarizabilities in such systems are dictated by the way the sodium atoms adsorb on the surface of fullerenes. One large metallic droplet of sodium atoms results to species with large hyperpolarizabilities of dipolar character. Smaller droplets adsorbed on the surface of C 60 deliver systems of large octupolar contributions. In both cases two synergic polarization mechanisms have been detected by means of the classical version of configuration interaction singles (CIS) sum-over-states approach and a natural transition orbital analysis. The first comprises charge transport from the fullerene to the adsorbed droplets and resembles the polarization process met in simple diatomic molecules. In this case, C 60 unconventionally functions as an electron donor at the excited states. The second, local in character, is related to the easily polarizable excess electrons maintained in the framework of the adsorbed clusters. From a certain point of view, such systems can be considered as hybrids that combine the basic characteristics of a classical donor/acceptor superstructure and systems with easily polarizable excess electrons. © 2012 American Chemical Society

Hirshfeld-based atomic population analysis of the B, N doping effect in zigzag graphene nanoribbons: π electron density as requirement to follow the B, N doping guidelines

International audienceIn this work, we present an atomic population study within the Fractional Occupation Hirshfeld-I (FOHI) scheme applied to several pristine, boron-, nitrogen- and B, N-doped non-periodic zigzag graphene nanoribbons (always using a double carbon replacement). To accomplish this task, we have considered the singlet–triplet energy gap as a criterion to check the most reliable electron density. B2PLYPD double-hybrid functional provides the most accurate relative energies in comparison with the other methods, but similar atomic populations are obtained in most cases. Moreover, in spite of the observed different behavior concerning the population of B, N dopants and their corresponding p- and n-type doping effects, the FOHI atomic populations are in excellent agreement with the widely accepted electronegative scale. Nevertheless, we propose to employ a more appropriate electron partitioning strategy taking into account the contribution of π-symmetric orbitals. It provides the expected population results according to doping guidelines. In any case, both kinds of populations describe in a similar way the mesomeric effects and the edge variations after replacing two carbons by either two boron or nitrogen atoms. On the contrary, the populations point out a different behavior when the systems are doped with one boron and one nitrogen simultaneously

Unleashing the quadratic nonlinear optical responses of graphene by confining white-graphene (h -BN) sections in its framework

cited By 23International audienceIn an attempt to diversify the options in designing graphene-based systems bearing large second order nonlinear optical (NLO) responses of octupolar and/or dipolar character, the subject of the quadratic NLO properties of hybrid boron nitride (BN) graphene flakes is opened up. State of the art ab initio and density functional theory methods applied on a toolbox of book-text octupolar and arbitrary dipolar planar hybrid h-BN-graphene nanosized systems reveal that by confining finite h-BN sections in the internal network of graphene, the capacity of the π-electron network of graphene species in delivering giant second order NLO responses could be fully exploited. Configuration interaction (CIS) and time-dependent density functional (TD) computations, within the sum-overstate (SOS) perturbational approach, expose that the prevailing (hyper)polarization mechanism, lying under the sizable computed octupolar hyperpolarizabilities, is fueled by alternating positive and negative atomic charges located in the internal part of the hybrid flakes, and more precisely at the BN/graphene intersections. This type of charge transfer mechanism distinguishes, in fact, the elemental graphene dipoles/octupoles we report here from other conventional NLO dipoles or octupoles. More interestingly, it is shown that by controlling the shape, size, and covering area of the h-BN domain (or domains), one can effectively regulate "à volonté" both the magnitudes and types of the second order NLO responses switching from dipolar to octupolar and vice versa. Especially in the context of the latter class of NLO properties, this communication brings into surface novel, graphene-based, octupolar planar or quasiplanar motifs. The take home message of this communication is summarized as follows: When the right BN segment is incorporated in the right section of the right graphene flake, systems of giant quadratic NLO octupolar and/or dipolar responses may emerge. © 2014 American Chemical Society

Quadratic nonlinear optical (NLO) properties of borazino (B3N3)-doped nanographenes

cited By 0International audienceBorazino-doped nanographenes belong to a special class of flat heteroaromatic networks comprising one or more fully formed borazino (B3N3) units in their framework. These systems carry the same number of electrons and feature similar structural forms as pristine nanographenes; however, they are characterized by different optoelectronic properties. As their full carbon analogues, borazino-doped graphene molecules could serve as excellent candidate molecules for flexible organic electronic and optical devices. In this study, we provided the results of a systematic study dealing with the effect of borazino units on the quadratic microscopic nonlinear optical (NLO) properties of finite graphene sections. These symmetry-dependent quantities describe the nonlinear polarization (hyperpolarization) of the electron cloud of molecules in the presence of external electric fields and they are associated with fundamental processes of extreme technological interest in the realm of nonlinear optics. More precisely, we investigated the evolution of the first dipole hyperpolarizability in several, purposely chosen, borazino-doped graphene flakes and ribbons, relying on long-range corrected density functional methods. Our results indicate that the presence of inorganic benzene in the honeycomb structure of graphene finite sections gives rise to some impressive structure-property variations driven by local electron delocalization effects. The take home message of this study suggests that borazino doping can deliver a vast assortment of nanographene molecules bearing amplified octupolar and/or dipolar NLO responses that can be fine-tuned by applying minor modifications in the structure and morphology of their edges. © 2017 The Royal Society of Chemistry