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  1. Article ; Online: Imaginary time correlations and the phaseless auxiliary field quantum Monte Carlo.

    Motta, M / Galli, D E / Moroni, S / Vitali, E

    The Journal of chemical physics

    2014  Volume 140, Issue 2, Page(s) 24107

    Abstract: The phaseless Auxiliary Field Quantum Monte Carlo (AFQMC) method provides a well established ...

    Abstract The phaseless Auxiliary Field Quantum Monte Carlo (AFQMC) method provides a well established approximation scheme for accurate calculations of ground state energies of many-fermions systems. Here we address the possibility of calculating imaginary time correlation functions with the phaseless AFQMC. We give a detailed description of the technique and test the quality of the results for static properties and imaginary time correlation functions against exact values for small systems.
    Language English
    Publishing date 2014-01-14
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3113-6
    ISSN 1089-7690 ; 0021-9606
    ISSN (online) 1089-7690
    ISSN 0021-9606
    DOI 10.1063/1.4861227
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Effects of self-seeding and crystal post-selection on the quality of Monte Carlo-integrated SFX data.

    Barends, Thomas / White, Thomas A / Barty, Anton / Foucar, Lutz / Messerschmidt, Marc / Alonso-Mori, Roberto / Botha, Sabine / Chapman, Henry / Doak, R Bruce / Galli, Lorenzo / Gati, Cornelius / Gutmann, Matthias / Koglin, Jason / Markvardsen, Anders / Nass, Karol / Oberthur, Dominik / Shoeman, Robert L / Schlichting, Ilme / Boutet, Sébastien

    Journal of synchrotron radiation

    2015  Volume 22, Issue 3, Page(s) 644–652

    Abstract: ... The partial intensities collected in this way are then combined in a scheme called Monte Carlo integration ... Carlo integration must also average out all variations in crystal quality, crystal size, X-ray beam ... for Monte Carlo integration to converge, resulting in more accurate data. This paper reports the results ...

    Abstract Serial femtosecond crystallography (SFX) is an emerging method for data collection at free-electron lasers (FELs) in which single diffraction snapshots are taken from a large number of crystals. The partial intensities collected in this way are then combined in a scheme called Monte Carlo integration, which provides the full diffraction intensities. However, apart from having to perform this merging, the Monte Carlo integration must also average out all variations in crystal quality, crystal size, X-ray beam properties and other factors, necessitating data collection from thousands of crystals. Because the pulses provided by FELs running in the typical self-amplified spontaneous emission (SASE) mode of operation have very irregular, spiky spectra that vary strongly from pulse to pulse, it has been suggested that this is an important source of variation contributing to inaccuracies in the intensities, and that, by using monochromatic pulses produced through a process called self-seeding, fewer images might be needed for Monte Carlo integration to converge, resulting in more accurate data. This paper reports the results of two experiments performed at the Linac Coherent Light Source in which data collected in both SASE and self-seeded mode were compared. Importantly, no improvement attributable to the use of self-seeding was detected. In addition, other possible sources of variation that affect SFX data quality were investigated, such as crystal-to-crystal variations reflected in the unit-cell parameters; however, these factors were found to have no influence on data quality either. Possibly, there is another source of variation as yet undetected that affects SFX data quality much more than any of the factors investigated here.
    Language English
    Publishing date 2015-05
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 2021413-3
    ISSN 1600-5775 ; 0909-0495
    ISSN (online) 1600-5775
    ISSN 0909-0495
    DOI 10.1107/S1600577515005184
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Exact ground state Monte Carlo method for Bosons without importance sampling.

    Rossi, M / Nava, M / Reatto, L / Galli, D E

    The Journal of chemical physics

    2009  Volume 131, Issue 15, Page(s) 154108

    Abstract: Generally "exact" quantum Monte Carlo computations for the ground state of many bosons make use ... ground state (PIGS) Monte Carlo. PIGS is based on a discrete imaginary time evolution of an initial wave ... Monte Carlo. On the other hand, a judicious choice of the initial wave function greatly improves ...

    Abstract Generally "exact" quantum Monte Carlo computations for the ground state of many bosons make use of importance sampling. The importance sampling is based either on a guiding function or on an initial variational wave function. Here we investigate the need of importance sampling in the case of path integral ground state (PIGS) Monte Carlo. PIGS is based on a discrete imaginary time evolution of an initial wave function with a nonzero overlap with the ground state, which gives rise to a discrete path which is sampled via a Metropolis-like algorithm. In principle the exact ground state is reached in the limit of an infinite imaginary time evolution, but actual computations are based on finite time evolutions and the question is whether such computations give unbiased exact results. We have studied bulk liquid and solid (4)He with PIGS by considering as initial wave function a constant, i.e., the ground state of an ideal Bose gas. This implies that the evolution toward the ground state is driven only by the imaginary time propagator, i.e., there is no importance sampling. For both phases we obtain results converging to those obtained by considering the best available variational wave function (the shadow wave function) as initial wave function. Moreover we obtain the same results even by considering wave functions with the wrong correlations, for instance, a wave function of a strongly localized Einstein crystal for the liquid phase. This convergence is true not only for diagonal properties such as the energy, the radial distribution function, and the static structure factor, but also for off-diagonal ones, such as the one-body density matrix. This robustness of PIGS can be traced back to the fact that the chosen initial wave function acts only at the beginning of the path without affecting the imaginary time propagator. From this analysis we conclude that zero temperature PIGS calculations can be as unbiased as those of finite temperature path integral Monte Carlo. On the other hand, a judicious choice of the initial wave function greatly improves the rate of convergence to the exact results.
    Language English
    Publishing date 2009-10-21
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3113-6
    ISSN 1089-7690 ; 0021-9606
    ISSN (online) 1089-7690
    ISSN 0021-9606
    DOI 10.1063/1.3247833
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Path integral Monte Carlo study of 4He clusters doped with alkali and alkali-earth ions.

    Galli, D E / Ceperley, D M / Reatto, L

    The journal of physical chemistry. A

    2011  Volume 115, Issue 25, Page(s) 7300–7309

    Abstract: Path integral Monte Carlo calculations of (4)He nanodroplets doped with alkali (Na(+), K(+) and Cs ...

    Abstract Path integral Monte Carlo calculations of (4)He nanodroplets doped with alkali (Na(+), K(+) and Cs(+)) and alkali-earth (Be(+) and Mg(+)) ions are presented. We study the system at T = 1 K and between 14 and 128 (4)He atoms. For all studied systems, we find that the ion is well localized at the center of the droplet with the formation of a "snowball" of well-defined shells of localized (4)He atoms forming solid-like order in at least the first surrounding shell. The number of surrounding helium shells (two or three) and the number of atoms per shell and the degree of localization of the helium atoms are sensitive to the type of ion. The number of (4)He atoms in the first shell varies from 12 for Na(+) to 18 for Mg(+) and depends weakly on the size of the droplet. The study of the density profile and of the angular correlations shows that the local solid-like order is more pronounced for the alkali ions with Na(+) giving a very stable icosahedral order extending up to three shells.
    Language English
    Publishing date 2011-06-30
    Publishing country United States
    Document type Journal Article
    ISSN 1520-5215
    ISSN (online) 1520-5215
    DOI 10.1021/jp200617a
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  5. Article: Dielectric response of periodic systems from quantum Monte Carlo calculations.

    Umari, P / Willamson, A J / Galli, Giulia / Marzari, Nicola

    Physical review letters

    2005  Volume 95, Issue 20, Page(s) 207602

    Abstract: ... in the quantum Monte Carlo formalism. We employ a many-body generalization for the electric-enthalpy functional ... diffusion quantum Monte Carlo calculations where the polarization's fixed point is estimated ...

    Abstract We present a novel approach that allows us to calculate the dielectric response of periodic systems in the quantum Monte Carlo formalism. We employ a many-body generalization for the electric-enthalpy functional, where the coupling with the field is expressed via the Berry-phase formulation for the macroscopic polarization. A self-consistent local Hamiltonian then determines the ground-state wave function, allowing for accurate diffusion quantum Monte Carlo calculations where the polarization's fixed point is estimated from the average on an iterative sequence, sampled via forward walking. This approach has been validated for the case of an isolated hydrogen atom and then applied to a periodic system, to calculate the dielectric susceptibility of molecular-hydrogen chains. The results found are in excellent agreement with the best estimates obtained from the extrapolation of quantum-chemistry calculations.
    Language English
    Publishing date 2005-11-11
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.95.207602
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  6. Article: Electron emission from diamondoids: a diffusion quantum Monte Carlo study.

    Drummond, N D / Williamson, A J / Needs, R J / Galli, G

    Physical review letters

    2005  Volume 95, Issue 9, Page(s) 96801

    Abstract: We present density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations designed ...

    Abstract We present density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations designed to resolve experimental and theoretical controversies over the optical properties of H-terminated C nanoparticles (diamondoids). The QMC results follow the trends of well-converged plane-wave DFT calculations for the size dependence of the optical gap, but they predict gaps that are 1-2 eV higher. They confirm that quantum confinement effects disappear in diamondoids larger than 1 nm, which have gaps below that of bulk diamond. Our QMC calculations predict a small exciton binding energy and a negative electron affinity (NEA) for diamondoids up to 1 nm, resulting from the delocalized nature of the lowest unoccupied molecular orbital. The NEA suggests a range of possible applications of diamondoids as low-voltage electron emitters.
    Language English
    Publishing date 2005-08-26
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.95.096801
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  7. Article: Quantum Monte Carlo calculations of nanostructure optical gaps: application to silicon quantum dots.

    Williamson, Andrew J / Grossman, Jeffrey C / Hood, Randolph Q / Puzder, Aaron / Galli, Giulia

    Physical review letters

    2002  Volume 89, Issue 19, Page(s) 196803

    Abstract: Quantum Monte Carlo (QMC) calculations of the optical gaps of silicon quantum dots ranging in size ...

    Abstract Quantum Monte Carlo (QMC) calculations of the optical gaps of silicon quantum dots ranging in size from 0 to 1.5 nm are presented. These QMC results are used to examine the accuracy of density functional (DFT) and empirical pseudopotential based calculations. The GW approximation combined with a solution of the Bethe-Salpeter equation performs well but is limited by its scaling with system size. Optical gaps predicted by DFT vary by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalism are found to be minimal in these systems.
    Language English
    Publishing date 2002-11-04
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.89.196803
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  8. Article: Quantum Monte Carlo study of the Su-Schrieffer-Heeger model in the high-level-doping concentration regime: Metal-insulator transition.

    Galli

    Physical review. B, Condensed matter

    1995  Volume 51, Issue 11, Page(s) 6863–6867

    Language English
    Publishing date 1995-03-15
    Publishing country United States
    Document type Journal Article
    ZDB-ID 209770-9
    ISSN 1095-3795 ; 1550-235X ; 0163-1829 ; 2469-9950 ; 1098-0121 ; 0556-2805
    ISSN (online) 1095-3795 ; 1550-235X
    ISSN 0163-1829 ; 2469-9950 ; 1098-0121 ; 0556-2805
    DOI 10.1103/physrevb.51.6863
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  9. Article ; Online: Regarding "Utility of Routine Postoperative Examination for Detecting Vaginal Cuff Dehiscence after Total Laparoscopic Hysterectomy".

    Uccella, Stefano / Casprini, Chiara / Bertoli, Francesca / Zorzato, Pier Carlo / Garzon, Simone / Galli, Liliana

    Journal of minimally invasive gynecology

    2024  

    Language English
    Publishing date 2024-02-10
    Publishing country United States
    Document type Letter
    ZDB-ID 2186934-0
    ISSN 1553-4669 ; 1553-4650
    ISSN (online) 1553-4669
    ISSN 1553-4650
    DOI 10.1016/j.jmig.2024.01.023
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  10. Article ; Online: Textile-Based Body Capacitive Sensing for Knee Angle Monitoring.

    Galli, Valeria / Ahmadizadeh, Chakaveh / Kunz, Raffael / Menon, Carlo

    Sensors (Basel, Switzerland)

    2023  Volume 23, Issue 24

    Abstract: Monitoring human movement is highly relevant in mobile health applications. Textile-based wearable solutions have the potential for continuous and unobtrusive monitoring. The precise estimation of joint angles is important in applications such as the ... ...

    Abstract Monitoring human movement is highly relevant in mobile health applications. Textile-based wearable solutions have the potential for continuous and unobtrusive monitoring. The precise estimation of joint angles is important in applications such as the prevention of osteoarthritis or in the assessment of the progress of physical rehabilitation. We propose a textile-based wearable device for knee angle estimation through capacitive sensors placed in different locations above the knee and in contact with the skin. We exploited this modality to enhance the baseline value of the capacitive sensors, hence facilitating readout. Moreover, the sensors are fabricated with only one layer of conductive fabric, which facilitates the design and realization of the wearable device. We observed the capability of our system to predict knee sagittal angle in comparison to gold-standard optical motion capture during knee flexion from a seated position and squats: the results showed an R
    MeSH term(s) Humans ; Knee ; Knee Joint ; Wearable Electronic Devices ; Movement ; Textiles
    Language English
    Publishing date 2023-12-06
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2052857-7
    ISSN 1424-8220 ; 1424-8220
    ISSN (online) 1424-8220
    ISSN 1424-8220
    DOI 10.3390/s23249657
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