Browsing by Author "Cardenas, Carlos"

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    Relationships between the third-order reactivity indicators in chemical density-functional theory
    (AMER INST PHYSICS, 2009) Cardenas, Carlos; Echegaray, Eleonora; Chakraborty, Debajit; Anderson, James S. M.; Ayers, Paul W.
    Relationships between third-order reactivity indicators in the closed system [N, v(r)], open system [mu, v(r)], and density [rho(r)] pictures are derived. Our method of derivation unifies and extends known results. Among the relationships is a link between the third-order response of the energy to changes in the density and the quadratic response of the density to changes in external potential. This provides a link between hyperpolarizability and the system's sensitivity to changes in electron density. The dual descriptor is a unifying feature of many of the formulas we derive.
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    Spin-active single photon emitters in hexagonal boron nitride from carbon-based defects
    (2023) Pinilla, Fernanda; Vasquez, Nicolas; Chacon, Ignacio; Maze, Jeronimo R.; Cardenas, Carlos; Munoz, Francisco
    Most single photon emitters in hexagonal boron nitride have been identified as carbon substitutional defects, forming donor-acceptor systems. Unlike the most studied bulk emitters (i.e. color centers in diamond), these defects have no net spin, or have a single unpaired spin. By means of density functional calculations, we show that two non-adjacent carbon substitutional defects of the same type (i.e. C-B-C-B, and C-N-C-N), can have a triplet groundstate. In particular, one of such defects has a zero phonon line energy of 2.5 eV, and its triplet state is nearly 0.5 eV more stable than its singlet. The mechanism behind the destabilization of the singlet state is related to a larger electrostatic repulsion of a symmetric wave function in a charged lattice.
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    Understanding chemical binding using the Berlin function and the reaction force
    (ELSEVIER, 2012) Chakraborty, Debajit; Cardenas, Carlos; Echegaray, Eleonora; Toro Labbe, Alejandro; Ayers, Paul W.
    We use the derivative of the electron density with respect to the reaction coordinate, interpreted through the Berlin binding function, to identify portions of the reaction path where chemical bonds are breaking and forming. The results agree with the conventional description for S(N)2 reactions, but they are much more general and can be used to elucidate other types of reactions also. Our analysis offers support for, and detailed information about, the use of the reaction force profile to separate the reaction coordinates into intervals, each with characteristic extents of geometry change and electronic rearrangement. (C) 2012 Elsevier B.V. All rights reserved.