Papers by David López Durán
Following recent works [1-3], we present path integral Monte Carlo (PIMC) calculations [4] for th... more Following recent works [1-3], we present path integral Monte Carlo (PIMC) calculations [4] for the structure and energetics of 4 He N nanodroplets doped with a single calcium atom. Sizes raging from 10 and 40 helium atoms were considered at temperatures of 1, 1.5 and 2 K. Simulations have been carried out using two different He-Ca interactions, Kleinekathöfer [5] and Lovallo [6], which reveal substantial discrepancies regarding the precise location of the Ca impurity with respect to the helium droplet and the total energy of the system. The different nature of the He-Ca and He-He interactions has been found to be crutial to understand the marked differences between the PIMC predictions in its classical and quantum mechanical versions.
9 software modules delivered to the E-CAM repository in the area of Electronic Structure respondi... more 9 software modules delivered to the E-CAM repository in the area of Electronic Structure responding to requests of users, and their documentation.
International Meeting on Atomic and Molecular Physics and Chemistry, Scuola Normale Superiore Pis... more International Meeting on Atomic and Molecular Physics and Chemistry, Scuola Normale Superiore Pisa, Italy, 12-14 September 2012
QSCP XIV - 14th International Workshop on Quantum Systems in Chemistry and Physics(San Lorenzo de... more QSCP XIV - 14th International Workshop on Quantum Systems in Chemistry and Physics(San Lorenzo del Escorial, 13-19 septiembre 2009)
The absence of magic numbers in bosonic 4 He clusters predicted by all theories since 1984 was ch... more The absence of magic numbers in bosonic 4 He clusters predicted by all theories since 1984 was challenged by high-resolution matter-wave diffraction experiments (Brühl et al., Phys. Rev. Lett. 92, 185301 (2004)). The observed magic numbers were explained in terms of enhanced growth rates of specific cluster sizes for which an additional excitation level, as calculated by Diffusion Monte Carlo, gets stabilized. The present theoretical study based on a simple interacting particle model of the He clusters, provides an alternative (more likely complementary) explanation: collisions between cluster atoms in excited states within the cluster lead to selective evaporation via an Auger process. The calculated magic numbers as well as the shape of the number distributions are in quite reasonable agreement with the experiments. Session Helium 1. Talk
Helium clusters have been successfully employed as an ideal environment to spectroscopically inve... more Helium clusters have been successfully employed as an ideal environment to spectroscopically investigate an ample list of impurities. For the case of atoms, the question of establishing solvation or surface location for the impurity in the helium droplet is an issue of great importance to further understand its behavior and the spectroscopic observations.
Trabajo presentado en COST Action CM1104 Reducible oxide chemistry, structure and functions - Wor... more Trabajo presentado en COST Action CM1104 Reducible oxide chemistry, structure and functions - Working Groups 1-Fundamentals and 2- Synthesis and Characterisation, celebrado en Zaragoza (Espana) del 28 al 30 de abril de 2014.
Trabajo presentado en el Meeting COST Action CM1104-Reducible oxide chemistry, structure and func... more Trabajo presentado en el Meeting COST Action CM1104-Reducible oxide chemistry, structure and functions, celebrado en Upsala (Suecia) del 6 al 8 de noviembre de 2013.
XXIX Reunion Bienal de la Real Sociedad Espanola de Fisica, Madrid 7-11 Julio. Resumenes de las c... more XXIX Reunion Bienal de la Real Sociedad Espanola de Fisica, Madrid 7-11 Julio. Resumenes de las comunicaciones, Volumen I, pg. 212-213 (2003)
La mejora sufrida en las tecnicas experimentales en los ultimos anos ha permitido observar los es... more La mejora sufrida en las tecnicas experimentales en los ultimos anos ha permitido observar los espectros de moleculas inmersas en gotas mas o menos grandes de Helio, tanto bosonico, 4He, como fermionico, 3He, y ponen de manifiesto propiedades cuanticas del entorno de una gran importancia. Como consecuencias de las diferencias isotopicas entre los atomos de 3He y 4He aparecen caracteristicas diferenciales y exclusivas entre uno y otro tipo de gotas. Los compuestos puros de 4He siempre aparecen ligados, independientemente del numero de atomos, y manifiestan rasgos de superfluidez a 2.2K. Por su parte, los de 3He estan ligados para complejos con mas de 30 atomos (Aprox.) y solo presentan superfluidez por debajo de 3 Mk. En el proyecto de tesis doctoral que ha sido llevado a cabo por D. David Lopez Duran, bajo la direccion del DR. Pablo Villarreal Herran y la Dra. Maria Pilar de Lara Castells, se ha desarrollado un modelo que arroja luz sobre el problema, teniendo en cuenta desde la din...
Trabajo presentado en el 50th Symposium on Theoretical Chemistry, celebrado en Viena (Austria) de... more Trabajo presentado en el 50th Symposium on Theoretical Chemistry, celebrado en Viena (Austria) del 14 al 18 de septiembre de 2014.
Trabajo presentado en Chemistry and Molecular Sciences and Technologies COST Action CM1104, celeb... more Trabajo presentado en Chemistry and Molecular Sciences and Technologies COST Action CM1104, celebrado en Viena (Austria) del 18 al 19 de abril de 2013.
The Journal of Chemical Physics, 2020
First-principles electronic structure calculations are now accessible to a very large community o... more First-principles electronic structure calculations are now accessible to a very large community of users across many disciplines thanks to many successful software packages, some of which are described in this special issue. The traditional coding paradigm for such packages is monolithic, i.e., regardless of how modular its internal structure may be, the code is built independently from others, essentially from the compiler up, possibly with the exception of linear-algebra and message-passing libraries. This model has endured and been quite successful for decades. The successful evolution of the electronic structure methodology itself, however, has resulted in an increasing complexity and an ever longer list of features expected within all software packages, which implies a growing amount of replication between different packages, not only in the initial coding but, more importantly, every time a code needs to be re-engineered to adapt to the evolution of computer hardware architecture. The Electronic Structure Library (ESL) was initiated by CECAM (the European Centre for Atomic and Molecular Calculations) to catalyze a paradigm shift away from the monolithic model and promote modularization, with the ambition to extract common tasks from electronic structure codes and redesign them as open-source libraries available to everybody. Such libraries include, e.g., "heavy-duty" ones that have the potential for a high degree of parallelisation and adaptation to novel hardware within them, thereby separating the sophisticated computer science aspects of performance optimization and reengineering from the computational science done by, e.g., physicists and chemists when implementing new ideas. We envisage that this modular paradigm will improve overall coding efficiency and enable specialists (whether they be computer scientists or computational scientists) to use their skills more effectively, and will lead to a more dynamic evolution of software in the community as well as lower barriers to entry for new developers. The model comes with new challenges, though. The building and compilation of a code based on many interdependent libraries (and their versions) is a much more complex task than that of a code delivered in a single self-contained package. Here we describe the state of the ESL, the different libraries it now contains, the short-and mid-term plans for further libraries, and the way the new challenges are faced. The ESL is a community initiative into which several pre-existing codes and their developers have contributed with their software and efforts, from which several codes are already benefiting, and which remains open to the community.
AIP Conference Proceedings, 2007
The intermolecular forces between atoms and molecules are of great importance in studies of solid... more The intermolecular forces between atoms and molecules are of great importance in studies of solids, liquids and clusters. Our current studies serve to bridge the gap between small cluster and large cluster limit.
ABSTRACT Instituto de Matemáticas y Física Fundamental (CSIC) Serrano 123, E-28006-Madrid (España... more ABSTRACT Instituto de Matemáticas y Física Fundamental (CSIC) Serrano 123, E-28006-Madrid (España) Resumen: En este trabajo, se ha simulado las transiciones de una molécula diatómical dentro de agregados bosónicos o fermiónicos de helio a muy bajas temperaturas. Para ello se ha utilizado una metodología de tipo químico-cuántico donde, una vez sustituidas las interacciones Coulombianas habituales por los correspondientes potenciales moleculares, la molécula juega el papel de los "núcleos" mientras que los átomos del solvente hacen de "electrones" a los que se les impone la simetría adecuada. En ambiente bosónico, el espectro salvo pequeños desplazamientos debidos a la presencia del solvente y junto al ensanchamiento producido por diversos mecanismos de relajación, presenta un perfil análogo al de la molécula aislada en fase gas. Todo ocurre como si la molécula estuviera rotando "libremente" dentro del agregado. Por el contrario, cuando el solvente es fermiónico, aparecen más ramas y además hay varias líneas que contribuyen en cada rama debido a la existencia de multipletes cuasi-degenerados de espín. Ambos factores dan lugar a una gran congestión del espectro, de forma que su perfil, muy ancho, carece de estructura y recuerda los espectros de moléculas pesadas sumergidas en líquidos. Tratamiento Mecano-cuántico El Hamiltoniano para un sistema He N —BC, en coordenadas tipo satélite {(r,R k)}donde r es el vector interdiatómico y R k son vectores desde el cm de BC a cada átomo de He, puede escribirse como [1,2] H = T r +U(r)+j 2 /2mr 2 +∑H k +∑V kl donde los tres primeros términos corresponden a BC, el cuarto es la suma de N Hamiltonianos triatómicos He—BC, y el último recoge todas las interacciones He-He (no sólo de potencial sino también de acoplamiento cinético). Congelando la distancia B-C y eligiendo un sistema de coordenadas cuyo eje Z es paralelo a r, se trata de resolver la ecuación de Schrödinger asociada a los "electrones", es decir, a los átomos de He, para el estado fundamental utilizando una metodología Hartree [3,4] o Hartree-Fock[1,2] dependiendo de su naturaleza bosónica o fermiónica, respectivamente. El autovalor correspondiente, que depende de r, se añade al potencial de BC, U(r), mientras que la autofunción se utiliza para promediar el término rotacional que depende de j 2 . Se obtiene así un Hamiltoniano efectivo para la molécula BC distorsionada por la presencia de los átomos del solvente, cuyos estados vibracionales (y energías asociadas) dependen, además del momento angular total J , de la proyección sobre el eje Z del momento angular orbital de los helios y, en su caso, del espín y de su proyección sobre el ya mencionado eje. Espectroscopía.
I International Meeting on Atomic and Molecualr Physics and Chemistry, Madrid, June 29-July 2, 2010
European Conference on Atoms, Molecules and Photons, Salamanca, Spain, 4 –9 July 2010Peer Reviewe
11th Iberian Joint Meeting on Atomic and Molecular Physics, Coimbra, Portugal, 19-22 June 2011. h... more 11th Iberian Joint Meeting on Atomic and Molecular Physics, Coimbra, Portugal, 19-22 June 2011. http://iber2011.fis.uc.pt/
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Papers by David López Durán