Correlation effects in positron-electron systems: A Quantum Monte-Carlo study

Harju, Ari; Barbiellini, B.; Siljamäki, S.; Nieminen, R.M.; Ortíz, Gerardo

doi:10.1007/bf02036273

Cited by 5 publications

(6 citation statements)

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“…Using a wave function with 8 variational parameters we found [7,8] similar performance to that in our previous examples. For instance, using the variance of the local energy as the cost function we found for hydrogen positronium (HPs) m 5, N i , 100.…”

supporting

confidence: 77%

“…Strong size dependent effects may occur [11] when E ep is computed as the total energy difference of the systems with and without the positron. To avoid this problem, we have calculated E ep by fitting over the range R the electron-positron pair distribution function from our simulation with an analytic form fulfilling the cusp and Friedel sum rule conditions [8], where Z is a coupling constant (0 , Z , 1) characterizing the charge of the positron, and c a fitting parameter [14]. This form is motivated by the fact that the shape of the screening cloud resembles that of a positronium, namely, exp͑2Zr͒ [15].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Harju¹,

Barbiellini²,

Siljamäki³

et al. 1997

Phys. Rev. Lett.

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confidence: 77%

mentioning

confidence: 99%

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Harju¹,

Barbiellini²,

Siljamäki³

et al. 1997

Phys. Rev. Lett.

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“…There seem to be uncertainties associated with the diffusion QMC method that go beyond the statistical uncertainties often quoted in the answer. This is exemplified by the calculation of Harju et al [42]. In this QMC calculation, a fixed core calculation gave a LiPs binding energy of 0.015 Hartree, while an ab initio calculation failed to predict binding.…”

Section: Results For Lipsmentioning

confidence: 95%

Improved binding energies for LiPs, e⁺Be, NaPs and e⁺Mg

Mitroy

Ryzhikh

2001

J. Phys. B: At. Mol. Opt. Phys.

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The stochastic variational method and its fixed core variant are applied to the calculation of lithium positride (LiPs), positronic beryllium (e + Be), sodium positride (NaPs) and positronic magnesium (e + Mg). The revised binding energy of LiPs was 0.012 341 Hartree, that for e + Be was 0.031 47 Hartree, that for NaPs was 0.008 419 Hartree and the binding energy for e + Mg was 0.015 612 Hartree. The binding energies for LiPs and e + Be are expected to be within 2% of the variational limit. The uncertainties in the NaPs and e + Mg binding energies are larger and these are expected to be within 10-15% of the variational limit.

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“…Using our smaller values of g(0) would reduce the enhancement factor and hence the overestimation of annihilation rates obtained with the positronic LDA [34]. Arponen & Pajanne [28] Lantto [26] Stachowiak & Lach [33] Apaja et al [35] Harju et al [36] FIG. 3: (Color online) Deviation of the contact PCF g(0) from the form gBN(0) of Boroński and Nieminen [29] together with other results in the literature [14,26,28,33,35,36].…”

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confidence: 96%

“…Arponen & Pajanne [28] Lantto [26] Stachowiak & Lach [33] Apaja et al [35] Harju et al [36] FIG. 3: (Color online) Deviation of the contact PCF g(0) from the form gBN(0) of Boroński and Nieminen [29] together with other results in the literature [14,26,28,33,35,36].…”

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confidence: 99%

Quantum Monte Carlo Study of a Positron in an Electron Gas

et al. 2011

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Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero weight above the Fermi momentum due to the cancellation of electron-electron and electron-positron correlation effects.PACS numbers: 78.70. Bj, 71.60.+z, 71.10.Ca, 02.70.Ss Electron-positron annihilation underlies both medical imaging with positron emission tomography (PET) and studies of materials using positron annihilation spectroscopy (PAS) [1]. Positrons entering a material rapidly thermalize and the majority annihilate with oppositespin electrons to yield pairs of photons at energies close to 0.511 MeV. In a PET scan, positrons are emitted by radionuclides in biologically active tracer molecules and the resulting annihilation radiation is measured to image the tracer concentration. The interaction of low-energy positrons with molecules is therefore of substantial experimental and theoretical interest [2]. PAS is used to investigate microstructures in metals, alloys, semiconductors, insulators [1], polymers [3], and nanoporous materials [4]. Positrons are repelled by the positively charged nuclei and tend to become trapped in voids within the material. The positron lifetime is measured as the interval between the detection of a photon emitted in the β + radioactive decay that produces the positron and the detection of the annihilation radiation [1]. The lifetime is characteristic of the region in which the positron settles, and PAS is a sensitive, nondestructive technique for characterizing the size, location, and concentration of voids in materials. Measuring the Doppler broadening of the annihilation radiation or the angular correlation between the two 0.511 MeV photons yields information about the momentum density (MD) of the electrons in the presence of the positron. These techniques may be used to investigate the Fermi surfaces of metals [5].The aim of PAS experiments is to investigate a host material without the changes induced by the positron. The positron is, however, an invasive probe which polarizes the electronic states of the material. Disentangling the properties of the host from the changes induced by the positron is a major theoretical challenge. Positrons in condensed matter may be modeled with two-component density functional theory (DFT) [6], in which the correlations are described by a functional of the electron and positron density components. Within the local density approximation (LDA), this functional is obtained from the difference ∆Ω between the energy of a homogeneous electron gas (HEG) with and without an immersed positron. ∆Ω is known as the relaxation energy, and is equal to the electron-positron correlation energy. Two-component DFT gives reasonable electron and positron densities, bu...

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Correlation effects in positron-electron systems: A Quantum Monte-Carlo study

Cited by 5 publications

References 25 publications

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Improved binding energies for LiPs, e⁺Be, NaPs and e⁺Mg

Quantum Monte Carlo Study of a Positron in an Electron Gas

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Correlation effects in positron-electron systems: A Quantum Monte-Carlo study

Cited by 5 publications

References 25 publications

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Stochastic Gradient Approximation: An Efficient Method to Optimize Many-Body Wave Functions

Improved binding energies for LiPs, e+Be, NaPs and e+Mg

Quantum Monte Carlo Study of a Positron in an Electron Gas

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Product

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Improved binding energies for LiPs, e⁺Be, NaPs and e⁺Mg