Walking paths from the low-symmetry hettotype to the high-symmetry aristotype structures of BX3 s... more Walking paths from the low-symmetry hettotype to the high-symmetry aristotype structures of BX3 sublattices in perovskite-like materials illustrate that the transformation can be either kinetically or thermodynamically controlled.
The electronic structure of the Mn: KZnF impurity system has been computed by means of a Hartree... more The electronic structure of the Mn: KZnF impurity system has been computed by means of a HartreeFockRoothaan cluster model. First, the Mn center has been simulated by the (MnF) unit in vacuo. Then, the effects of the KZnF lattice have been included in the cluster ...
A better understanding of the effects of thermal and pressure on the wide gap SiC semiconductor i... more A better understanding of the effects of thermal and pressure on the wide gap SiC semiconductor is necessary for both (i) an improvement of the performance of this compound in...
La Quimica Teorica ha conseguido encauzar la solucion multielectronica de la ecuacion de Schrodin... more La Quimica Teorica ha conseguido encauzar la solucion multielectronica de la ecuacion de Schrodinger de moleculas y solidos hacia una descripcion en el espacio real tridimensional donde el concepto de enlace quimico puede definirse de modo inequivoco. Utiliza el analisis topologico de funciones escalares basadas en la densidad electronica para visualizar y definir regiones de interes quimico: atomos, pares enlazantes, pares solitarios, etc., identificando lineas de enlace e interacciones no covalentes. Se logra asi conciliar la Quimica Cuan- tica con la teoria de Lewis y el modelo de repulsion de pares de electrones de la capa de valencia.
Structural, thermodynamic and electronic properties of CdGeAs 2 with chalcopyrite structure are i... more Structural, thermodynamic and electronic properties of CdGeAs 2 with chalcopyrite structure are investigated in the framework of density functional theory. We employ the linear combination of atomic orbitals method with the Gaussian basis sets and present the results for the equation of state, the Gr üneisen constant, the electronic band structure and the pressure coefficients of the valence and conduction levels in CdGeAs 2.
ABSTRACT El estudio de los efectos de las presiones elevadas sobre los seres vivos ha necesitado ... more ABSTRACT El estudio de los efectos de las presiones elevadas sobre los seres vivos ha necesitado de una serie de avances técnicos para poder desarrollarse. A pesar de ser muy conscientes de la presión hidrostática que sufren las profundidades marinas, fue muy difícil conocer qué organismos las poblaban. Desde la antigüedad se tenían pruebas indirectas a través de las capturas de los pescadores y mediante la aparición esporádica de “monstruos” abisales. La observación directa tuvo que esperar a mediados del siglo XX para permitir el acceso mediante batiscafos a profundidades superiores a las que podían alcanzar los buzos, extendiendo la exploración desde las primeras decenas de metros hasta varios miles de metros de profundidad. De esta forma se extendió el rango de presiones cuyos efectos se podían observar de 1 a 100 MPa. Las observaciones y estudios de microorganismos provenientes de grandes profundidades marinas han sufrido mayores retrasos que el estudio de metazooos. En este capítulo se expondrá el desarrollo de los estudios de los fondos oceánicos, y el aislamiento de microorganismos obtenidos de todo tipo de ambientes expuestos a alta presión. También se describirán las peculiaridades de estos microorganismos, viendo que algunas son compartidas por otros microorganismos adaptados a distintos ambientes extremos. Se hará un repaso de los efectos de la alta presión en los elementos celulares, de cómo esto puede resultar letal para los seres vivos y de cómo algunos han desarrollado adaptaciones. Destacaremos el potencial biotecnológico de los extremófilos, revisando algunas posibles utilidades derivadas de los microorganismos piezófilos. Se terminará presentando los estudios destinados a eliminar microorganismos mediante la aplicación de alta presión, principalmente en alimentos y cómo algunas variables, como el estado de crecimiento del microorganismo o el pH del medio, pueden afectar a la letalidad causada.
ELF superbasins (dark-yellow stick and ball circuits) reveal how borate clusters (green and red s... more ELF superbasins (dark-yellow stick and ball circuits) reveal how borate clusters (green and red spheres) play the role of crystal defects interrupting the electric conductivity of metallic silver (grey spheres).
The rhombohedral layered MgIn2Se4 undergoes a pressure-induced phase transition to an inverse spi... more The rhombohedral layered MgIn2Se4 undergoes a pressure-induced phase transition to an inverse spinel one, loses its van der Waals interactions, and becomes more covalent.
Abstract Two distinct points on the potential energy curve (PEC) of a pairwise interaction, the z... more Abstract Two distinct points on the potential energy curve (PEC) of a pairwise interaction, the zero‐energy crossing point and the point where the stretching force constant vanishes, allow us to anticipate the range of possible distances between two atoms in diatomic, molecular moieties and crystalline systems. We show that these bond‐stability boundaries are unambiguously defined and correlate with topological descriptors of electron‐density‐based scalar fields, and can be calculated using generic PECs. Chemical databases and quantum‐mechanical calculations are used to analyze a full set of diatomic bonds of atoms from the s‐p main block. Emphasis is placed on the effect of substituents in C−C covalent bonds, concluding that distances shorter than 1.14 Å or longer than 2.0 Å are unlikely to be achieved, in agreement with ultra‐high‐pressure data and transition‐state distances, respectively. Presumed exceptions are used to place our model in the correct framework and to formulate a conjecture for chained interactions, which offers an explanation for the multimodal histogram of O−H distances reported for hundreds of chemical systems.
We present a general computational scheme to extend the spinodal equation of state [García Baonza... more We present a general computational scheme to extend the spinodal equation of state [García Baonza et al., Phys. Rev. B 51, 28 (1995)] to the interpretation of the cell parameters response to hydrostatic pressure in orthogonal lattices. As an important example, we analyze the pressure (p)–volume (V)–temperature (T) data of the rutile phase of TiO2. We show that results of ab initio perturbed ion calculations and very recent x-ray-diffraction experiments of isothermal compression on this system closely follow the spinodal conduct. The computational scheme permits the incorporation of temperature effects in the static calculation as well as in the room-temperature experimental data. Overall, we find highly consistent results and good theory-experiment agreement for a significant series of observables, including structural parameters, p-V diagram, bulk modulus, linear compressibilities, and thermal-expansion coefficient. The observed discrepancies in the pressure first derivative of the...
ABSTRACT We present the results of an investigation on the pressure behavior of structural, bondi... more ABSTRACT We present the results of an investigation on the pressure behavior of structural, bonding and vibrational properties of β- and γ-C3N4 phases. Emphasis is focused on the trends of the calculated properties along the A3N4 (A: C, Si, Ge) family. Geometry optimizations and electronic structure calculations are carried out in the framework of the local density functional theory using a planewave-pseudopotential scheme. The equilibrium cell geometry, the isothermal bulk modulus and its pressure derivatives have been evaluated for the two phases in a pressure range up to 400 GPa. The Bader’s Atoms in Molecules formalism is applied to characterize the chemical bonding and the atomic contributions to the bulk compressibility in β- and γ-A3N4 crystals. The calculated stability diagram reveals the occurrence of a hypothetical β-C3N4→γ-C3N4 phase transition around 370 GPa. Γ-point harmonic vibrational modes are computed at selected pressures within the density functional perturbation theory approach. In agreement with recent theoretical calculations, the comparison of the computed Raman vibrational frequencies with experimental estimations for β-C3N4 raises doubts on a previously reported synthesis of this structure. Pressure effects on the vibrational frequencies inform of a reduction of the P63∕m symmetry of the β phase at pressures around 60 GPa and contribute to look into the mechanical stability of the γ phase.
Walking paths from the low-symmetry hettotype to the high-symmetry aristotype structures of BX3 s... more Walking paths from the low-symmetry hettotype to the high-symmetry aristotype structures of BX3 sublattices in perovskite-like materials illustrate that the transformation can be either kinetically or thermodynamically controlled.
The electronic structure of the Mn: KZnF impurity system has been computed by means of a Hartree... more The electronic structure of the Mn: KZnF impurity system has been computed by means of a HartreeFockRoothaan cluster model. First, the Mn center has been simulated by the (MnF) unit in vacuo. Then, the effects of the KZnF lattice have been included in the cluster ...
A better understanding of the effects of thermal and pressure on the wide gap SiC semiconductor i... more A better understanding of the effects of thermal and pressure on the wide gap SiC semiconductor is necessary for both (i) an improvement of the performance of this compound in...
La Quimica Teorica ha conseguido encauzar la solucion multielectronica de la ecuacion de Schrodin... more La Quimica Teorica ha conseguido encauzar la solucion multielectronica de la ecuacion de Schrodinger de moleculas y solidos hacia una descripcion en el espacio real tridimensional donde el concepto de enlace quimico puede definirse de modo inequivoco. Utiliza el analisis topologico de funciones escalares basadas en la densidad electronica para visualizar y definir regiones de interes quimico: atomos, pares enlazantes, pares solitarios, etc., identificando lineas de enlace e interacciones no covalentes. Se logra asi conciliar la Quimica Cuan- tica con la teoria de Lewis y el modelo de repulsion de pares de electrones de la capa de valencia.
Structural, thermodynamic and electronic properties of CdGeAs 2 with chalcopyrite structure are i... more Structural, thermodynamic and electronic properties of CdGeAs 2 with chalcopyrite structure are investigated in the framework of density functional theory. We employ the linear combination of atomic orbitals method with the Gaussian basis sets and present the results for the equation of state, the Gr üneisen constant, the electronic band structure and the pressure coefficients of the valence and conduction levels in CdGeAs 2.
ABSTRACT El estudio de los efectos de las presiones elevadas sobre los seres vivos ha necesitado ... more ABSTRACT El estudio de los efectos de las presiones elevadas sobre los seres vivos ha necesitado de una serie de avances técnicos para poder desarrollarse. A pesar de ser muy conscientes de la presión hidrostática que sufren las profundidades marinas, fue muy difícil conocer qué organismos las poblaban. Desde la antigüedad se tenían pruebas indirectas a través de las capturas de los pescadores y mediante la aparición esporádica de “monstruos” abisales. La observación directa tuvo que esperar a mediados del siglo XX para permitir el acceso mediante batiscafos a profundidades superiores a las que podían alcanzar los buzos, extendiendo la exploración desde las primeras decenas de metros hasta varios miles de metros de profundidad. De esta forma se extendió el rango de presiones cuyos efectos se podían observar de 1 a 100 MPa. Las observaciones y estudios de microorganismos provenientes de grandes profundidades marinas han sufrido mayores retrasos que el estudio de metazooos. En este capítulo se expondrá el desarrollo de los estudios de los fondos oceánicos, y el aislamiento de microorganismos obtenidos de todo tipo de ambientes expuestos a alta presión. También se describirán las peculiaridades de estos microorganismos, viendo que algunas son compartidas por otros microorganismos adaptados a distintos ambientes extremos. Se hará un repaso de los efectos de la alta presión en los elementos celulares, de cómo esto puede resultar letal para los seres vivos y de cómo algunos han desarrollado adaptaciones. Destacaremos el potencial biotecnológico de los extremófilos, revisando algunas posibles utilidades derivadas de los microorganismos piezófilos. Se terminará presentando los estudios destinados a eliminar microorganismos mediante la aplicación de alta presión, principalmente en alimentos y cómo algunas variables, como el estado de crecimiento del microorganismo o el pH del medio, pueden afectar a la letalidad causada.
ELF superbasins (dark-yellow stick and ball circuits) reveal how borate clusters (green and red s... more ELF superbasins (dark-yellow stick and ball circuits) reveal how borate clusters (green and red spheres) play the role of crystal defects interrupting the electric conductivity of metallic silver (grey spheres).
The rhombohedral layered MgIn2Se4 undergoes a pressure-induced phase transition to an inverse spi... more The rhombohedral layered MgIn2Se4 undergoes a pressure-induced phase transition to an inverse spinel one, loses its van der Waals interactions, and becomes more covalent.
Abstract Two distinct points on the potential energy curve (PEC) of a pairwise interaction, the z... more Abstract Two distinct points on the potential energy curve (PEC) of a pairwise interaction, the zero‐energy crossing point and the point where the stretching force constant vanishes, allow us to anticipate the range of possible distances between two atoms in diatomic, molecular moieties and crystalline systems. We show that these bond‐stability boundaries are unambiguously defined and correlate with topological descriptors of electron‐density‐based scalar fields, and can be calculated using generic PECs. Chemical databases and quantum‐mechanical calculations are used to analyze a full set of diatomic bonds of atoms from the s‐p main block. Emphasis is placed on the effect of substituents in C−C covalent bonds, concluding that distances shorter than 1.14 Å or longer than 2.0 Å are unlikely to be achieved, in agreement with ultra‐high‐pressure data and transition‐state distances, respectively. Presumed exceptions are used to place our model in the correct framework and to formulate a conjecture for chained interactions, which offers an explanation for the multimodal histogram of O−H distances reported for hundreds of chemical systems.
We present a general computational scheme to extend the spinodal equation of state [García Baonza... more We present a general computational scheme to extend the spinodal equation of state [García Baonza et al., Phys. Rev. B 51, 28 (1995)] to the interpretation of the cell parameters response to hydrostatic pressure in orthogonal lattices. As an important example, we analyze the pressure (p)–volume (V)–temperature (T) data of the rutile phase of TiO2. We show that results of ab initio perturbed ion calculations and very recent x-ray-diffraction experiments of isothermal compression on this system closely follow the spinodal conduct. The computational scheme permits the incorporation of temperature effects in the static calculation as well as in the room-temperature experimental data. Overall, we find highly consistent results and good theory-experiment agreement for a significant series of observables, including structural parameters, p-V diagram, bulk modulus, linear compressibilities, and thermal-expansion coefficient. The observed discrepancies in the pressure first derivative of the...
ABSTRACT We present the results of an investigation on the pressure behavior of structural, bondi... more ABSTRACT We present the results of an investigation on the pressure behavior of structural, bonding and vibrational properties of β- and γ-C3N4 phases. Emphasis is focused on the trends of the calculated properties along the A3N4 (A: C, Si, Ge) family. Geometry optimizations and electronic structure calculations are carried out in the framework of the local density functional theory using a planewave-pseudopotential scheme. The equilibrium cell geometry, the isothermal bulk modulus and its pressure derivatives have been evaluated for the two phases in a pressure range up to 400 GPa. The Bader’s Atoms in Molecules formalism is applied to characterize the chemical bonding and the atomic contributions to the bulk compressibility in β- and γ-A3N4 crystals. The calculated stability diagram reveals the occurrence of a hypothetical β-C3N4→γ-C3N4 phase transition around 370 GPa. Γ-point harmonic vibrational modes are computed at selected pressures within the density functional perturbation theory approach. In agreement with recent theoretical calculations, the comparison of the computed Raman vibrational frequencies with experimental estimations for β-C3N4 raises doubts on a previously reported synthesis of this structure. Pressure effects on the vibrational frequencies inform of a reduction of the P63∕m symmetry of the β phase at pressures around 60 GPa and contribute to look into the mechanical stability of the γ phase.
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Papers by j. manuel Recio