Quasiparticle calculations

Flybertsen M S and Louie S G 1985 First-principles theory of quasiparticles Calculation of band gaps in semiconductors and insulators Phys. Rev. Lett. 55 1418... 

Judicious use of the approximations discussed here has the potential to facilitate accurate quasiparticle calculations on molecular systems of unprecedented size. These techniques provide a number of new options for the calculation of EADEs with advantageous compromises between computational cost and reliability. 

Quasiparticle calculations on nucleic acid fragments with one or two bases yield many final states that may be obtained from anionic states by electron detachment. The QVOS procedure introduces only minor errors while providing large improvements in computational efficiency. Propagator calculations on an anion with two thymine bases amend the order of final states predicted by Hartree-Fock orbital energies and exhibit the need for correlated methods in interpreting anion photoelectron spectra of nucleic acid fragments. 

Quasiparticles Calculations of Band Gaps in Semiconductors and Insulators. 

If there are many valence protons and neutrons present in the nucleus, traditional shell model calculations lead to insurmountable difficulties. Fortunately, the Bardeen-Cooper-Schrieffer (BCS) theory provides a good approximation method to the seniority-zero shell model, and allows to describe very complex nuclei, too. In the BCS quasiparticle calculations long chains of nuclei can be treated in a relatively simple way. The method was first applied in the theory of superconductivity by Bardeen et al. (1957), then used for nuclear physics by Bohr et al. (1958), Soloviev (1958), and Belyaev (1959). The quasiparticle concept was introduced into nuclear physics by Valatin (1958) and Bogoliubov (1958). The theory is explained in detail in several textbooks (Lawson 1980 Ring and Schuck 1980 Soloviev 1981 Heyde 1990 Nilsson and Ragnarsson 1995 Fenyes 2002). 

Aulbur, W. G., Jonsson, L., 8c Wilkins, J. W (2000). Quasiparticle calculations in solids. Solid State Physics, 54,1. 

On the basis of the quasiparticle calculations in the GW approximation performed on LaH3 including the f states and the d states, Chang et al. (2001) concluded that LaH3 is a band... 

Figure B3.2.1. The band structure of hexagonal GaN, calculated using EHT-TB parameters detemiined by a genetic algorithm [23]. The target energies are indicated by crosses. The target band structure has been calculated with an ab initio pseudopotential method using a quasiparticle approach to include many-particle corrections [194].

More advanced teclmiques take into account quasiparticle corrections to the DFT-LDA eigenvalues. Quasiparticles are a way of conceptualizing the elementary excitations in electronic systems. They can be detennined in band stmcture calculations that properly include the effects of exchange and correlation. In the... 

This idea that the heat was transfered by a random walk was used early on by Einstein [21] to calculate the thermal conductance of crystals, but, of course, he obtained numbers much lower than those measured in the experiment. As we now know, crystals at low enough T support well-defined quasiparticles—the phonons—which happen to carry heat at these temperatures. Ironically, Einstein never tried his model on the amorphous solids, where it would be applicable in the / fp/X I regime. 

The fermionic determinant Detiow averaged over instanton anti-instanton positions, orientations and sizes leads to a partition function of light quarks Z. Then the properties of the hadrons and their interactions are concentrated in the QCD effective action written in terms of the quasiparticles. This approach leads to the Diakonov-Petrov(DP) effective action (D.I. Diakonov et.al., 1996). It was shown that DP effective action is a good tool in the chiral limit but fails beyond this limit, checked by the calculations of the axial-anomaly low energy theorems (M.M. Musakhanov et.al., 1997 E. Di Salvo et.al., 1998). 

The characteristic line emanating from Tc is naturally related to the critical line Tc(fi) enclosing the hadronic phase. The comparison, in Figure 4, of our result for the curvature of the critical line at g - 0, which can be calculated in lattice QCD [13], is a nontrivial and successful test of the extension of the quasiparticle approach to g > 0. 

Figure 5. The quark number susceptibility for Nf = 2, calculated from the quasiparticle model with the same parameters as in Figs. 3 and 4, for several chemical potentials compared to the lattice data [14] at /u = 0.

Development of methods related to DFT that can treat this situation accurately is an active area of research where considerable progress is being made. Two representative examples of this kind of work are P. Rinke, A. Qteish, J. Neugebauer, and M. Scheffler, Exciting Prospects for Solids Exact Exchange Based Functional Meet Quasiparticle Energy Calculations, Phys. Stat. Sol. 245 (2008), 929, and J. Uddin, J. E. Peralta, and G. E. Scuseria, Density Functional Theory Study of Bulk Platinum Monoxide, Phys. Rev. B, 71 (2005), 155112. 

Further we present the results of our calculations of the Li- ike iGplasma satellite lines on the basis of QED PT with ab initio zeroth-order approximation for three-quasiparticle systems, together with the optimized Dirac-Fock results and experimental data for comparison. In Table 4 there are displayed the experimental value (A) for wavelength (in A) of the Ti-like lines dielectron satellites to the ls So-ls3p Pi line of radiation in the K plasma, and the corresponding theoretical results (B) PT on 1/Z (C) QED PT (our data) (D) calculation by the AUTOJOLS method, and (E) MCDF [12, 21],... 

Usually, the electronic thermal conductance re can be calculated from the Wiedemann - Franz law, re TG/e2. However, as shown in Ref. [8, 9] for the ballistic limit f > d, this law gives a wrong result for Andreev wires if one uses an expression for G obtained for a wire surrounded by an insulator. Andreev processes strongly suppress the single electron transport for all quasiparticle trajectories except for those which have momenta almost parallel to the wire thus avoiding Andreev reflection at the walls. The resulting expression for the thermal conductance... 

An immediate consequence of symmetry is the nature of the quasiparticle spectrum. The density of states p(co) can be calculated from the knowledge of the quasi-particle energies. For singlet states Ek,+ = Ek, with... 

Here Eck, (Evki) are the quasiparticle energies, calculated within the GW approximation, of the states (ck) and (vk ). In terms of the eigenvalues and eigenvectors of the excitonic Hamiltonian, namely ... 

Figure one shows the results of calculations of 3gb and 131Sn, one-quasiparticle nuclides. The calculated levels agree very well with experimental excitation states. Figure 1 also shows results using the bare KK interaction and with the addition of a weak QQ potential determined in the two-quasiparticle nucli-... 

Figure 1. Results for calculations on the one quasiparticle nuclides. Experimental states are labeled with the nucleus. Calculated states are shown to the right, labeled with the effective interaction that was used.

Figures 3a-3d. These figures show the dependence of the calculated states on the pairing strength for the three quasiparticle nuclei. Only experimentally accessible states are shown...

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