Person:
García Baonza, Valentín

First Name

Valentín

Last Name

García Baonza

URI

https://hdl.handle.net/20.500.14352/76144

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Químicas

Area

Química Física

Identifiers

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Now showing 1 - 10 of 13

Computational Modeling of Tensile Stress Effects on the Structure and Stability of Prototypical Covalent and Layered Materials
(Nanomaterials, 2019) Chorfi, Hocine; Lobato Fernández, Álvaro; Boudjada, Fahima; Salvadó, Miguel A.; Franco, Ruth; García Baonza, Valentín; Recio, J. Manuel
Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS 2 . Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes.
Linear, Non-Conjugated Cyclic and Conjugated Cyclic Paraphenylene under Pressure
(Molecules, 2019) Peña-Álvarez, Miriam; Fanetti, Samuele; Falsini, Naomi; Novelli, Giulia; Casado, Juan; García Baonza, Valentín; Taravillo Corralo, Mercedes; Parsons, Simon; Bini, Roberto; Citroni, Margherita
The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), and non-conjugated cyclic systems with two hydrogenated phenylenes (H4[n]CPP). Particularly, the systems of interest in this work are [6]LPP, [12]- and [6]CPP and H4[6]CPP. This work combines Raman and infrared spectroscopies with absorption and fluorescence (one- and two-photon excitations) measured as a function of pressure up to maximum of about 25 GPa. Unprecedented crystallographic pressure-dependent results are shown on H4[n]CPP, revealing intramolecular π-π interactions upon compression. These intramolecular interactions justify the H4[n]CPP singular optical properties with increasing fluorescence lifetime as a function of pressure.
Project number: 242
Laboratorio integrado de prácticas de simulación de fundamentos y procesos químicos con fluidos supercríticos
(2019) Calvo Garrido, Lourdes; Cabañas Poveda, Albertina; Pando García-Pumarino, Concepción; García Baonza, Valentín; González Mac-Dowell, Luis; Tirado Armesto, Diego Felipe; Cuadra Mendoza, Isaac Alfonso; Menéndez Carbajosa, Alicia Marta; Calvo Garrido, María Lourdes
El objetivo del proyecto ha sido crear un laboratorio integrado de prácticas de simulación relacionadas con fundamentos termodinámicos y procesos con fluidos supercríticos, destinado a los alumnos de Química e Ingeniería Química.
Caracterización multianalítica (SEM-EDX, microsonda electrónica y espectroscopía Raman) de los cóndrulos y de la matriz de la condrita carbonácea de Allende
(Geogaceta, 2018) López Acosta, David; Martínez Frías, Jesús; García Baonza, Valentín; Lunar Hernández, María Del Rosario
Allende es un ejemplo emblemático de condrita carbonácea caída en Pueblito de Allende (México) en 1969. Este meteorito es especialmente importante debido a su composición primitiva, como uno de los principales representantes de los primeros estadios del Sistema Solar. En este estudio se ha llevado a cabo una nueva caracterización multianalítica de esta condrita, centrada en la mineralogía y la geoquímica de los cóndrulos y la matriz empleando varias técnicas: microscopía óptica, SEM-EDX, microsonda electrónica y espectroscopía Raman, siendo especialmente relevante estaúltima, que ha demostrado ser de gran utilidad aportando información sobre el mineral y su estructura.
Infrared spectroscopic study of the formation of fossil resin analogs with temperature using trans-communic acid as precursor
(Microchemical Journal, 2018) Rodríguez Montoro, Óscar; Lobato Fernández, Álvaro; García Baonza, Valentín; Taravillo Corralo, Mercedes
For million years resin exudates have undergone chemical alterations by heat, pressure, radiation, water, oxygen, microorganisms, and have suffered processes of sedimentation and diagenesis. These agents have affected the organic functional groups present in the terpenes of the resins, giving rise to what we nowadays know as fossil resins. In this work, we try to get further insight in the chemical formation of fossil resins. As the simulation of the natural process is quite complex, we have focused on the temperature induced reactivity of the trans-communic acid, the main component of the Class I resins. Using this terpene derivate as a very basic model of a resin exudate, we have monitored their thermal changes by infrared spectroscopy, Differential Scanning Calorimetry and Thermogravimetric Analysis within the range of 25 to 340 °C. The temperature-induced transformation, both in presence and absence of inert atmosphere, is discussed on the basis of the reactivity of the conjugated double-bond, the exocyclic bond and the carboxylic acid group present in the trans-communic acid. The results obtained in these series of experiments agree with the maturation scheme accepted in the literature for natural resins, i.e. an initial cross-linked polymerization and a subsequent maturation reaction. From combined DSC/TGA and infrared spectroscopy results, we conclude that chemical changes produced in the trans-communic acid in the range 130–175 °C may mimic the initial polymerization-like process in the natural resins, whereas those produced between 180 and 340 °C seem to correspond to the maturation pathways described in the literature for fossil resins Class Ib. Spectral assignment of the most relevant infrared-active modes of the trans-communic acid at 25 °C is also provided with the aid of Density Functional Theory calculations.
Generalized Stress-Redox Equivalence: A Chemical Link between Pressure and Electronegativity in Inorganic Crystals
(Inorganic Chemistry, 2019) Lobato Fernández, Álvaro; Osman, Hussien ; Salvadó, Miguel ; Pertierra, Pilar; Vegas, Ángel; García Baonza, Valentín; Recio, José Manuel
The crystal structure of many inorganic compounds can be understood as a metallic matrix playing the role of a host lattice in which the nonmetallic atomic constituents are located, the Anions in Metallic Matrices (AMM) model stated. The power and utility of this model lie in its capacity to anticipate the actual positions of the guest atoms in inorganic crystals using only the information known from the metal lattice structure. As a pertinent test-bed for the AMM model, we choose a set of common metallic phases along with other nonconventional or more complex structures (face-centered cubic (fcc) and simple cubic Ca, CsCl-type BaSn, hP4-K, and fcc-Na) and perform density functional theory electronic structure calculations. Our topological analysis of the chemical pressure (CP) scalar field, easily derived from these standard first-principles electronic computations, reveals that CP minima appear just at the precise positions of the nonmetallic elements in typical inorganic crystals presenting the above metallic subarrays: CaF2, rock-salt and CsCl-type phases of CaX (X = O, S, Se, Te), BaSnO3, K2S, and NaX (X = F, Cl, Br, I). A theoretical basis for this correlation is provided by exploring the equivalence between hydrostatic pressure and the oxidation (or reduction) effect induced by the nonmetallic element on the metal structure. Indeed, our CP analysis leads us to propose a generalized stress-redox equivalence that is able to account for the two main observed phenomena in solid inorganic compounds upon crystal formation: (i) the expansion or contraction experienced by the metal structure after hosting the nonmetallic element while its topology is maintained and (ii) the increasing or decreasing of the effective charge associated with the anions in inorganic compounds with respect to the charge already present in the interstices of the metal network. We demonstrate that a rational explanation of this rich behavior is provided by means of Pearson-Parr’s electronegativity equalization principle.
Temperature effects on the friction-like mode of graphite
(Theoretical Chemical Accounts, 2017) Menéndez, Cesar; Lobato Fernández, Álvaro; García Baonza, Valentín; Recio, José Manuel
Since the anharmonicity of the vibrational mode related to the relative rigid motion of graphene layers plays a decisive role in the friction behavior of graphite, a quantitative account of the temperature dependence of the frequency of this E2G(1) mode is worth to be investigated. Starting with the solution of the Morse quantum-mechanical oscillator, a relationship between the populated averaged vibrational quantum number and temperature is proposed. This expression is applied to our previous computed Morse fittings describing the anharmonic potential of this mode (Menéndez et al. in Phys Rev B 93:144112-1–144112-9, 2016) with the aim at providing the available vibrational energy at different pressures and temperatures. We show that the average vibrational quantum number decreases under pressure but the available vibrational energy is almost independent on pressure at a given temperature. As a result, the calculated temperature coefficient shows that inter-layer friction in graphite lowers as temperature increases with a similar trend regardless the pressure applied.
Chemical pressure–chemical knowledge: squeezing bonds and lone pairs within the valence shell electron pair repulsion model
(Physical Chemistry Chemical Physics, 2019) Lobato Fernández, Álvaro; Osman, Hussien; Salvadó, Miguel; Taravillo Corralo, Mercedes; García Baonza, Valentín; Recio, José Manuel
The valence shell electron pair repulsion (VSEPR) model is a demanding testbed for modern chemical bonding formalisms. The challenge consists in providing reliable quantum mechanical interpretations of how chemical concepts such as bonds, lone pairs, electronegativity, or hypervalence influence (or modulate) molecular geometries. Several schemes have been developed thus far to visualize and characterize these effects; however, to the best of our knowledge, no scheme has yet incorporated the analysis of the premises derived from the ligand close-packing (LCP) extension of the VSEPR model. Within the LCP framework, the activity of the lone pairs of the central atom and ligand–ligand repulsions constitute the two key features necessary to explain certain controversial molecular geometries that do not conform to the VSEPR rules. Considering the dynamical picture obtained when electron local forces at different nuclear configurations are evaluated from first-principles calculations, we investigate the chemical pressure distributions in a variety of molecular systems, namely, electron-deficient molecules (BeH2, BH3, BF3), several AX3 series (A: N, P, As; X: H, F, Cl), SO2, ethylene, SF4, ClF3, XeF2, and nonequilibrium configurations of water and ammonia. Our chemical pressure maps clearly reveal space regions that are totally consistent with the molecular and electronic geometries predicted by VSEPR and provide a quantitative correlation between the lone pair activity of the central atom and electronegativity of ligands, which are in agreement with the LCP model. Moreover, the analysis of the kinetic and potential energy contributions to the chemical pressure allows us to provide simple explanations on the connection between ligand electronegativity and electrophilic/nucleophilic character of the molecules, with interesting implications in their potential reactivity. NH3, NF3, SO2, BF3, and the inversion barrier of AX3 molecules are selected to illustrate our findings.
Theoretical (DFT) and experimental (Raman and FTIR) spectroscopic study on communic acids, main components of fossil resins
(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019) Rodríguez Montoro, Óscar; Tortajada Pérez, José; Lobato Fernández, Álvaro; García Baonza, Valentín; Taravillo Corralo, Mercedes
The objective of this work is to establish a spectral assignment of several communic acids. The most significant vibrational modes of three stereoisomers of communic acids [trans-, cis-, and iso- (or mirceo-)] are presented. They are showed throughout experimental Raman and IR spectra, and on the basis on calculations with Density Functional Theory (DFT) and the assignment of the spectral bands of different resins found in the literature. These three communic acids studied are the most important isomers present in the scaffold of the fossil resins Class I, as monomers or co-polymerized according to several authors. These kinds of terpenes are used as starting material, for example, for the synthesis of the fungicide and compounds bioactives. In a novel way, it is reported jointly the assignment of the experimental Infrared and Raman modes together with theoretical modes, since normally the authors tend to focus on one or another spectroscopic technique only. These results can be used as a reference for distinguishing amber from less matured resins as copal, determining the local origin of archaeological fossilized resins. Moreover, they will serve as help to differentiate between real and imitation ambers.
Local and solvation pressures in aqueous solutions of ethylenediamine probed by Raman spectroscopy
(Physical Chemistry Chemical Physics, 2016) Cáceres Alonso, María Mercedes; Lobato Fernández, Álvaro; Mendoza, Nubia; Jimenez Bonales, Laura; García Baonza, Valentín
Raman spectra of 1,2-ethylenediamine (EDA) in aqueous solutions are used to demonstrate that EDA molecules experience an anti–gauche conformational change resulting from the interactions with water. The observed Raman shift reveals a compressive (hydrophobic) effect of water on both methylene and amino groups of EDA. Raman spectra of EDA at high pressures are used as reference to quantify the intermolecular EDA–H2O interactions in terms of local pressures. These results are compared with macroscopic solvation pressures calculated from the cohesive energy parameter. We compare and discuss all our observations with available computational and experimental studies.