Velocity autocorrelation by quantum simulations for direct parameter-free computations of the neutron cross sections. II. Liquid deuterium

Autor(en)

E. Guarini, M. Neumann, U. Bafile, M. Celli, D. Colognesi, S. Bellissima, E. Farhi, Y. Calzavara

Abstrakt

Very recently we showed that quantum centroid molecular dynamics (CMD) simulations of the velocity autocorrelation function provide, through the Gaussian approximation (GA), an appropriate representation of the single-molecule dynamic structure factor of liquid H-2, as witnessed by a straightforward absolute-scale agreement between calculated and experimental values of the total neutron cross section (TCS) at thermal and epithermal incident energies. Also, a proper quantum evaluation of the self-dynamics was found to guarantee, via the simple Skold model, a suitable account of the distinct (intermolecular) contributions that influence the neutron TCS of para-H-2 for low-energy neutrons (below 10 meV). The very different role of coherent nuclear scattering in D-2 makes the neutron response from this liquid much more extensively determined by the collective dynamics, even above the cold neutron range. Here we show that the Skold approximation maintains its effectiveness in producing the correct cross section values also in the deuterium case. This confirms that the true key point for reliable computational estimates of the neutron TCS of the hydrogen liquids is, together with a good knowledge of the static structure factor, the modeling of the self part, which must take into due account quantum delocalization effects on the translational single-molecule dynamics. We demonstrate that both CMD and ring polymer molecular dynamics (RPMD) simulations provide similar results for the velocity autocorrelation function of liquid D-2 and, consequently, for the neutron double differential cross section and its integrals. This second investigation completes and reinforces the validity of the proposed quantum method for the prediction of the scattering law of these cryogenic liquids, so important for cold neutron production and related condensed matter research.

Organisation(en)

Computergestützte Physik und Physik der Weichen Materie

Externe Organisation(en)

Università degli Studi di Firenze, Consiglio Nazionale delle Ricerche, Institut Laue-Langevin (ILL)

Journal

Physical Review B

Band

93

Anzahl der Seiten

8

ISSN

1098-0121

DOI

https://doi.org/10.1103/PhysRevB.93.224302

Publikationsdatum

06-2016

Peer-reviewed

Ja

ÖFOS 2012

103015 Kondensierte Materie, 103029 Statistische Physik

Schlagwörter

ASJC Scopus Sachgebiete

Electronic, Optical and Magnetic Materials, Condensed Matter Physics

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/4f82cea8-6ba2-4774-8027-50ba7138c29c