2,598 research outputs found
Combining symmetry collective states with coupled cluster theory: Lessons from the Agassi model Hamiltonian
The failures of single-reference coupled cluster for strongly correlated
many-body systems is flagged at the mean-field level by the spontaneous
breaking of one or more physical symmetries of the Hamiltonian. Restoring the
symmetry of the mean-field determinant by projection reveals that coupled
cluster fails because it factorizes high-order excitation amplitudes
incorrectly. However, symmetry-projected mean-field wave functions do not
account sufficiently for dynamic (or weak) correlation. Here we pursue a merger
of symmetry projection and coupled cluster theory, following previous work
along these lines that utilized the simple Lipkin model system as a testbed [J.
Chem. Phys. 146, 054110 (2017)]. We generalize the concept of a
symmetry-projected mean-field wave function to the concept of a symmetry
projected state, in which the factorization of high-order excitation amplitudes
in terms of low-order ones is guided by symmetry projection and is not
exponential, and combine them with coupled cluster theory in order to model the
ground state of the Agassi Hamiltonian. This model has two separate channels of
correlation and two separate physical symmetries which are broken under strong
correlation. We show how the combination of symmetry collective states and
coupled cluster is effective in obtaining correlation energies and order
parameters of the Agassi model throughout its phase diagram
Performance, emissions, and physical characteristics of a rotating combustion aircraft engine
The RC2-75, a liquid cooled two chamber rotary combustion engine (Wankel type), designed for aircraft use, was tested and representative baseline (212 KW, 285 BHP) performance and emissions characteristics established. The testing included running fuel/air mixture control curves and varied ignition timing to permit selection of desirable and practical settings for running wide open throttle curves, propeller load curves, variable manifold pressure curves covering cruise conditions, and EPA cycle operating points. Performance and emissions data were recorded for all of the points run. In addition to the test data, information required to characterize the engine and evaluate its performance in aircraft use is provided over a range from one half to twice its present power. The exhaust emissions results are compared to the 1980 EPA requirements. Standard day take-off brake specific fuel consumption is 356 g/KW-HR (.585 lb/BHP-HR) for the configuration tested
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