Ab initio study of the one-dimensional H-bonded ferroelectric CsH2PO4

We studied the microscopic mechanism of the paraelectric-ferroelectric (PE-FE) phase transition of CsH2PO4 (CDP) by means of first-principles electronic structure calculations. The calculated structural parameters in the PE and FE phases as well as the total spontaneous polarization Ps obtained with the Berry phase formalism for CDP are in good agreement with experiments. The main contribution to Ps originates from a large yx component of the calculated Born effective-charge tensor for the disordered protons. Moreover, this component is ≈2.7 times larger than the zx component of the proton effective-charge tensor relevant to the polarization in the H-bonded FE KH2PO4 (KDP). This is the main feature that compensates the different number of protons per formula unit involved in the phase transitions for CDP and KDP to give close values for their measured Ps. Correlations among protons and heavy atoms along chains in the b direction lead to larger instabilities for the global and local FE distortions in CDP and its deuterated counterpart DCDP. We conclude that the tunneling particle is a dressed proton (deuteron) in agreement with experiments and with recent ab initio results for KDP.Fil: Lasave, Jorge Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Koval, Sergio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Ring population statistics in an ice lattice model

We calculate the distribution probability of hexagonal six-site rings in the disordered state of a cubic or hexagonal ice lattice model with ice rules perfectly obeyed. The mean-field distribution obtained is in significant agreement with those, slightly different among them, obtained by Monte Carlo simulations of the cubic or hexagonal model. The results are discussed in connection with the equilibrium and non-equilibrium transition from disorder to ferroelectric proton order.Fil: Khosravi, Ali. The Abdus Salam. International Centre for Theoretical Physics; Italia. The Abdus Salam; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Lasave, Jorge Augusto. The Abdus Salam. International Centre for Theoretical Physics; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. The Abdus Salam; ItaliaFil: Koval, Sergio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Tosatti, Erio. The Abdus Salam; Italia. The Abdus Salam. International Centre for Theoretical Physics; Italia. Consiglio Nazionale delle Ricerche; Itali

Concertedness and solvent effects in multiple proton transfer reactions: the formic acid dimer in solution

Using an approach based on a hybrid quantum mechanical-molecular mechanical (QM-MM) strategy, the case of double proton transfer (PT) in the formic acid dimer, embedded in a cluster of polar solvent molecules was examined. The aim was to determine the influence of external constraints and solvent fluctuations on the energetic and dynamic aspects of multiple proton transfer phenomena in solution. The presence of the solvent reduced the barrier height by a factor seemingly independent of the solvent-free value. Further, it was found that the dynamics of PT events is deeply connected to the dynamics of the solvent.Fil: Kohanoff, Jorge Jose. The Abdus Salam; Italia. The Queens University of Belfast; Irlanda. The Abdus Salam. International Centre for Theoretical Physics; ItaliaFil: Koval, Sergio Fabian. The Abdus Salam. International Centre for Theoretical Physics; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. The Abdus Salam; ItaliaFil: Estrin, Dario Ariel. The Abdus Salam; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. The Abdus Salam. International Centre for Theoretical Physics; ItaliaFil: Laria, Daniel Hector. Universidad de Buenos Aires; Argentina. Comisión Nacional de Energía Atómica; Argentina. The Abdus Salam; Italia. The Abdus Salam. International Centre for Theoretical Physics; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Abashkin, Y.. NCI-Frederick Cancer Research and Development Center; Estados Unido

Raman phonon spectrum of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7

The Raman spectrum of Ba2CuGe2O7, a tetragonal insulator which develops Dzyaloshinskii-Moriya helical magnetism below TN=3.2K, has been detected at temperatures varying from 300 to 80 K in a single crystal, with the radiation polarized either in the ab plane or along the c axis of its tetragonal cell. Twenty-nine phonon lines out of the 35 allowed by the Raman selection rules for the present geometry were observed, and their vibrational frequencies were found in overall good agreement with those provided by shell-model calculations. Together with the previous report on the infrared-active phonons [A. Nucara, Phys. Rev. B 90, 014304 (2014)PRBMDO1098-012110.1103/PhysRevB.90.014304], the present study provides an exhaustive description, both experimental and theoretical, of the lattice dynamics in Ba2CuGe2O7.Fil: Capitanio, Fabiana Lia. Università degli studi di Roma ; ItaliaFil: Koval, Sergio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Fittipaldi, Diego Rodrigo. Universita di Salerno; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Caramazza, S.. Università degli studi di Roma ; ItaliaFil: Paris, E.. Istituto Italiano di Tecnologia. Center for Life Nano Science at Sapienza; ItaliaFil: Mohamed, W. S.. Università degli studi di Roma ; ItaliaFil: Lorenzana, J.. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma ; ItaliaFil: Nucara, A.. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma ; ItaliaFil: Rocco, L.. Consiglio Nazionale delle Ricerche; Italia. Universita di Salerno; ItaliaFil: Vecchione, A.. Consiglio Nazionale delle Ricerche; Italia. Universita di Salerno; ItaliaFil: Postorino, P.. Università degli studi di Roma ; ItaliaFil: Calvani, P.. Università degli studi di Roma ; Italia. Consiglio Nazionale delle Ricerche; Itali

Ab initio and shell model studies of structural, thermoelastic and vibrational properties of SnO 2 under pressure

The pressure dependences of the structural, thermoelastic and vibrational properties of SnO2 in its rutile phase are studied, as well as the pressure-induced transition to a CaCl2-type phase. These studies have been performed by means of ab initio (AI) density functional theory calculations using the localized basis code SIESTA. The results are employed to develop a shell model (SM) for application in future studies of nanostructured SnO2. A good agreement of the SM results for the pressure dependences of the above properties with the ones obtained from present and previous AI calculations as well as from experiments is achieved. The transition is characterized by a rotation of the Sn-centered oxygen octahedra around the tetragonal axis through the Sn. This rotation breaks the tetragonal symmetry of the lattice and an orthorhombic distortion appears above the critical pressure Pc. A zone-center phonon of B1g symmetry in the rutile phase involves such rotation and softens on approaching Pc. It becomes an Ag mode which stabilizes with increasing pressure in the CaCl2 phase. This behavior, together with the softening of the shear modulus (C11 −C12)/2 related to the orthorhombic distortion, allows a precise determination of a value for Pc. An additional determination is provided by the splitting of the basal plane lattice parameters. Both the AI and the experimentally observed softening of the B1g mode are incomplete, indicating a small discontinuity at the transition. However, all results show continuous changes in volume and lattice parameters, indicating a second-order transition. All these results indicate that there should be sufficient confidence for the future employment of the shell model.Fil: Casali, Ricardo Antonio. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Departamento de Física; ArgentinaFil: Lasave, Jorge Augusto. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Caravaca, M. A.. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Departamento de Física; ArgentinaFil: Koval, Sergio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Cs.exactas Ingenieria y Agrimensura. Escuela de Cs.exactas y Naturales; ArgentinaFil: Ponce Altamirano, Claudio Ariel. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Departamento de Física; ArgentinaFil: Migoni, Ricardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Cs.exactas Ingenieria y Agrimensura. Escuela de Cs.exactas y Naturales; Argentin

Ab initio study of the structure, isotope effects, and vibrational properties in KDP crystals

The lattice dynamics of potassium dihydrogen phosphate (KDP) and its deuterated analog DKDP was studied via first-principles DFT calculations. A thorough assessment of the quality of a wide range of functionals supplemented with the approximate inclusion of quantum nuclear effects indicated that the nonlocal van der Waals functional vdW-DF [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)PRLTAO0031-900710.1103/PhysRevLett.92.246401; J. Klimeš et al., Phys. Rev. B 83, 195131 (2011)PRBMDO1098-012110.1103/PhysRevB.83.195131] produces the best agreement with structural data for both compounds. This enabled the calculation of full phonon dispersions in the ferroelectric phase, and hence the phonon density of states and specific heat, in very good agreement with experimental data. Phonon bands and especially modes at the Γ point of the Brillouin zone were classified according to their vibrational pattern. This allowed for the assignment of stretching and bending modes of the hydrogen bonds. Internal modes involving the phosphate units were identified at lower frequencies, while the lowest-lying modes were those involving the K+ ion. These assignments were used to interpret infrared and Raman spectra along the c axis and in the perpendicular plane. Phonon modes calculated at the Γ point showed two types of instabilities. One was a normal mode polarized along the c axis of the crystal, while the other corresponded to a twofold-degenerate mode polarized in the perpendicular plane. The former gives rise to a spontaneous polarization in the ferroelectric phase at low temperatures by coupling to an optical K+-H2PO4- stretching mode, consistently with a significant off-diagonal Born effective charge on the hydrogen atoms. A mode describing the opposite rotation of neighboring PO4 tetrahedra was also found to couple strongly to the ferroelectric mode, as this modulates the O-O distance, which determines the barrier for proton transfer. The present study suggests that a minimal model to describe isotope effects in KDP should involve at least three fully coupled vibrational modes.Fil: Menchón, Rodrigo Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Colizzi, G.. The Queens University of Belfast; IrlandaFil: Johnston, C.. The Queens University of Belfast; IrlandaFil: Torresi, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lasave, Jorge Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Koval, Sergio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Kohanoff, Jorge Jose. The Queens University of Belfast; IrlandaFil: Migoni, Ricardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Outcomes in Newly Diagnosed Atrial Fibrillation and History of Acute Coronary Syndromes: Insights from GARFIELD-AF

BACKGROUND: Many patients with atrial fibrillation have concomitant coronary artery disease with or without acute coronary syndromes and are in need of additional antithrombotic therapy. There are few data on the long-term clinical outcome of atrial fibrillation patients with a history of acute coronary syndrome. This is a 2-year study of atrial fibrillation patients with or without a history of acute coronary syndromes