Density functional calculations and analysis of the crystal structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Pb</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>P</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>

Suewattana, Malliga; Singh, David J.; Fornari, Marco

doi:10.1103/physrevb.75.172105

Cited by 9 publications

(10 citation statements)

References 24 publications

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“…This has a physical interpretation in terms of cross gap hybridization between occupied O 2p states and unoccupied Bi 6p states. [76,[80][81][82][83]. Intuitively, the larger the energy gap, the lower the polarization should be.…”

Section: Ferroelectric Propertiesmentioning

confidence: 99%

Hybrid functional study of proper and improper multiferroics

Stroppa

Picozzi

2010

Phys. Chem. Chem. Phys.

156

109

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We present a detailed study of the structural, electronic, magnetic and ferroelectric properties of prototypical proper and improper multiferroic (MF) systems such as BiFeO(3) and orthorhombic HoMnO(3), respectively, within density functional theory (DFT) and using the Heyd-Scuseria-Ernzerhof hybrid functional (HSE). By comparing our results with available experimental data as well as with state-of-the-art GW calculations, we show that the HSE formalism is able to account well for the relevant properties of these compounds and it emerges as an accurate tool for predictive first-principles investigations on multiferroic systems. We show that effects beyond local and semilocal DFT approaches (as provided by HSE) are necessary for a realistic description of MFs. For the electric polarization, a decrease is found for MFs with magnetically-induced ferroelectricity, such as HoMnO(3), where the calculated polarization changes from approximately 6 muC cm(-2) using Perdew-Burke-Ernzerhof (PBE) to approximately 2 muC cm(-2) using HSE. However, for proper MFs, such as BiFeO(3), the polarization slightly increases upon introduction of exact exchange. Our findings therefore suggest that a general trend for the HSE correction to bare density functional cannot be extracted; rather, a specific investigation has to be carried out on each compound.

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Section: Ferroelectric Propertiesmentioning

confidence: 99%

Hybrid functional study of proper and improper multiferroics

Stroppa

Picozzi

2010

Phys. Chem. Chem. Phys.

156

109

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“…As a result, there is no finite basis set error per se in DMC. There are presently two main flavors of the phaseless AFQMC method, corresponding to two different choices of the one-electron basis: (i) planewave with norm-conserving pseudopotential (as widely adopted in solid state physics), 9,11 and (ii) Gaussian type basis sets (the standard in quantum chemistry). 10 In planewave AFQMC, convergence to the basis set limit is easily controlled, as in DFT calculations, using the plane wave cutoff energy E cut .…”

Section: Introductionmentioning

confidence: 99%

Pressure-induced diamond toβ-tin transition in bulk silicon: A quantum Monte Carlo study

2009

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The pressure-induced structural phase transition from diamond to β-tin in silicon is an excellent test for theoretical total energy methods. The transition pressure provides a sensitive measure of small relative energy changes between the two phases (one a semiconductor and the other a semimetal). Experimentally, the transition pressure is well characterized. Density-functional results have been unsatisfactory. Even the generally much more accurate diffusion Monte Carlo method has shown a noticeable fixed-node error. We use the recently developed phaseless auxiliary-field quantum Monte Carlo (AFQMC) method to calculate the relative energy differences in the two phases. In this method, all but the error due to the phaseless constraint can be controlled systematically and driven to zero. In both structural phases we were able to benchmark the error of the phaseless constraint by carrying out exact unconstrained AFQMC calculations for small supercells. Comparison between the two shows that the systematic error in the absolute total energies due to the phaseless constraint is well within 0.5mEh/atom. Consistent with these internal benchmarks, the transition pressure obtained by the phaseless AFQMC from large supercells is in very good agreement with experiment.PACS numbers: 64.70. 61.50.Ks, 71.15.Nc.

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“…This is easy to see from the 1/N term which, at sufficiently large r s , causes ǫ c to diverge. To guide the analysis in this region, we use the plane-wave auxiliary-field (AF) QMC method [11,12] to directly calculate E for FS jellium systems. At small r s , the correlation energy obtained is in excellent agreement with that derived from Eq.…”

mentioning

confidence: 99%

“…Our first application of the method is to a model system in the opposite limit. We consider a "molecular solid" with P 2 in a periodic supercell, treated by the plane-wave AF QMC method [11,12]. Because of the low-density "vapor" region and the variation in density, the system provides a challenging test for the correction method.…”

mentioning

confidence: 99%

“…50 for 16 atoms) and average the results [16]. The plane-wave AF QMC method [11,12] was used, in which any k-point can be included by a simple modification to the one-particle ba- (4) 1.135(4) 54 1.184 (9) 1.189(10) 1.143(10) expt 1.129 (6) sis. Although our pseudopotential has a Ne-core, DFT tests with various pseudopotentials verified that it is sufficient for the cohesive energy (consistent with Ref.…”

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confidence: 99%

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Finite-Size Correction in Many-Body Electronic Structure Calculations

2008

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Finite-size (FS) effects are a major source of error in many-body (MB) electronic structure calculations of extended systems. A method is presented to correct for such errors. We show that MB FS effects can be effectively included in a modified local density approximation calculation. A parametrization for the FS exchange-correlation functional is obtained. The method is simple and gives post-processing corrections that can be applied to any MB results. Applications to a model insulator (P2 in a supercell), to semiconducting Si, and to metallic Na show that the method delivers greatly improved FS corrections.PACS numbers: 02.70. Ss, 71.15.Nc, Realistic many-body (MB) calculations for extended systems are needed to accurately treat systems where the otherwise successful density functional theory (DFT) approach fails. Examples range from strongly correlated materials, such as high-temperature superconductors, to systems with moderate correlation, for instance where accurate treatments of bond-stretching or bond-breaking are required. DFT or Hartree Fock (HF), which are effectively independent-particle methods, routinely exploit Bloch's theorem in calculations for extended systems. In crystalline materials, the cost of the calculations depends only on the number of atoms in the periodic cell, and the macroscopic limit is achieved by a quadrature in the Brillouin zone, using a finite number of k-points. MB methods, by contrast, cannot avail themselves of this simplification. Instead calculations must be performed using increasingly larger simulation cells (supercells). Because the Coulomb interactions are long-ranged, finite-size (FS) effects tend to persist to large system sizes, making reliable extrapolations impractical. The resulting FS errors in state-of-the-art MB quantum simulations often can be more significant than statistical and other systematic errors. Reducing FS errors is thus a key to broader applications of MB methods in real materials, and the subject has drawn considerable attention [1,2].In this paper, we introduce an external correction method, which is designed to approximately include FS corrections in modified DFT calculations with finite-size functionals. The method is simple, and provides postprocessing corrections applicable to any previously obtained MB results. Conceptually, it gives a consistent framework for relating FS effects in MB and DFT calculations, which is important if the two methods are to be seamlessly interfaced to bridge length scales. The correction method is applied to a model insulator (P 2 in a supercell), to semiconducting bulk Si, and to Na metal. We find that it consistently removes most of the FS errors, leading to rapid convergence of the MB results to the infinite system.We write the N -electron MB Hamiltonian in a supercell as (Rydberg atomic units are used throughout):where the ionic potential on i can be local or non-local, and r i is an electron position. The Coulomb interaction V FS between electrons depends on the supercell size and shape, due to modificatio...

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Density functional calculations and analysis of the crystal structure ofPb2P2O7

Cited by 9 publications

References 24 publications

Hybrid functional study of proper and improper multiferroics

Hybrid functional study of proper and improper multiferroics

Pressure-induced diamond toβ-tin transition in bulk silicon: A quantum Monte Carlo study

Finite-Size Correction in Many-Body Electronic Structure Calculations

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