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Titolo: VARIATIONAL THEORY OF BULK HE4 WITH SHADOW WAVEFUNCTIONS  GROUNDSTATE AND THE PHONONMAXONROTON SPECTRUM
Autore: MORONI S; GALLI DE; FANTONI S; REATTO L;
 Indirizzi:
 ABDUS SALAM INT CTR THEORET PHYS,STRADA COSTIERA 11 I34014 TRIESTE ITALY IST NAZL FIS MAT I20133 MILAN ITALY UNIV MILAN,DIPARTIMENTO FIS I20133 MILAN ITALY SCUOLA INT SUPER STUDI AVANZATI I34014 TRIESTE ITALY
 Titolo Testata:
 Physical review. B, Condensed matter
fascicolo: 2,
volume: 58,
anno: 1998,
pagine: 909  924
 SICI:
 01631829(1998)58:2<909:VTOBHW>2.0.ZU;2#
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 QUANTUM MONTECARLO; SUPERFLUID HE4; PAIR CORRELATIONS; LIQUIDHE4; EXCITATIONS; HELIUM;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Science Citation Index Expanded
 Citazioni:
 41
 Recensione:
 Indirizzi per estratti:



 Citazione:
 S. Moroni et al., "VARIATIONAL THEORY OF BULK HE4 WITH SHADOW WAVEFUNCTIONS  GROUNDSTATE AND THE PHONONMAXONROTON SPECTRUM", Physical review. B, Condensed matter, 58(2), 1998, pp. 909924
Abstract
We apply an efficient optimization scheme to shadow wave functions (SWF's) for the ground state of liquid and solid He4. Results improve on previous variational energies in both phases. In the liquid, the gain over a wave function with only pair and triplet correlations increases with density, providing a quantitative estimate of the increasing effect of higherorder correlations. The discrepancy with the exact groundstate energy is nearly constant over a wide range of densities, yielding excellent estimates for the equilibrium, freezing,and melting densities. The optimal SWF's can be represented with high precision by densityindependent sets of variational parameters for the liquid and the solid phases. An extensive study of groundstate properties demonstrates the uniformly good quality of the variational description afforded by the optimized SWF's. Based on such an accurate representation of the ground state, and including the correct longrange correlations due to the zeropoint motion of phonons, we compute the excitation spectrum and the strength of the single quasiparticle excitation peak. While the use of optimized SWF's confirms the accuracy of previous studies in the maxonroton region, the proper treatment of longrange correlations allows us to extend to the phonon region the agreement betweentheory and experiment. We simulate relatively large systems in order to explore the longwavelength regime in detail. Even down to wave vectors where the excitation energy exhibits a highly linear dispersion, which would suggest a harmonic phonon mode, the kinetic and potential energies of the excitation are far from verifying equipartition. This result is supported by additional diffusion Monte Carlo simulations within the fixed node approximation. We locate the onset of the harmonicregime for the longwavelength excitations at an extremely small value of the wave vector, k less than or similar to 0.05 Angstrom(1). [S01631829(98)00126X].
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Documento generato il 26/11/20 alle ore 11:00:22