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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Mixed Stochastic-Deterministic Approach for Many-Body Perturbation Theory Calculations

Here, we present an approach for GW calculations of quasiparticle energies with quasi-quadratic scaling by approximating high-energy contributions to the Green's function in its Lehmann representation with effective stochastic vectors. The method is easy to implement without altering the GW code, converges rapidly with stochastic parameters, and treats systems of various dimensionality and screening response. Our calculations on a 5.75° twisted MoS 2 bilayer show how large-scale GW methods include geometry relaxations and electronic correlations on an equal basis in structurally nontrivial materials.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Perturbation theory of structure in classical liquid mixtures: Application to metallic systems near phase separation

The partial structure factors of classical simple liquid mixtures near phase separation are dicussed. The theory is developed for particles interacting through pair potentials, and is thus appropriate both to insulating fluids, and also to metallic systems if these may be described by an effective ion-ion pair interaction. The motivation arose from consideration of metallic liquid mixtures, in which resistive anomalies have been observed near phase separation. A mean field theory correction appropriate to 3 pair potential for the effects of correlated motions in the reference fluid is studied. The work is cast in terms of functions which are closely related to the direct correlation functions of Ornstein and Zernike. The results are qualitatively in accord with physical expectations. Quantitative agreement with experiment seems to turn on the selection of the hard core reference potential in terms of the metallic effective pair potential. It is suggested that the present effective pair potentials are perhaps not properly used to calculate the metallic structure factors at long wavelength.

Henderson, R. L.↗
NASA NTRS1974

A unified approach for the application of general perturbation theories to the artificial satellite problem

An Encke-type method is developed as well as a variation of parameters method, both of which use a non-Keplerian reference orbit. The regularized time is used in the numerical integration and the optimum value of n is found for each type of orbit investigated. Accuracy and computation time comparisons are made with a classical Cowell method. It should be noted that the element formulations developed and tested were found to be exceptionally numerically stable in the sense that it was possible to achieve numerical consistency order of very long integration periods - a property not available with the Cowell formulation - and therefore these formulations may be helpful for high precision calculations.

Alfriend, K. T.↗
NASA NTRS1991

Secular perturbation theory and computation of asteroid proper elements

A new theory for the calculation of proper elements is presented. This theory defines an explicit algorithm applicable to any chosen set of orbits and accounts for the effect of shallow resonances on secular frequencies. The proper elements are computed with an iterative algorithm and the behavior of the iteration can be used to define a quality code.

Milani, Andrea↗