A comparison between two ab intio methods for coupled cluster calculations : CCSD(T) vs. CR-CC(2,3)
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Cool white dwarfs are extremely useful as cosmochronometers. However, current models do not provide a good enough fit for the atmospheres of these stars. As a part of a current proposal to provide an improved fit for the spectra of cool white dwarfs, this paper explores two methods for Coupled Cluster calculations, CCSD(T) and CR-CC(2,3). The former is the current "gold standard", however, CR-CC(2,3) has shown promise as a less computationally stressful method. Using a He-H2 system, expansion coefficients were derived from both methods producing identical data. However, when the intramolecular distance for H2was varied the energy difference between the two methods showed a quadratic increase. It was determined that for the He-H2 system studied, numerically the methods were equally accurate; however, the efficiency of the calculations would define which one should be should be used with this system. More complex systems need to be studied to draw broader conclusions about the utility of each of the methods.