Spin-flip approach method

In order to see the difference in the two approaches, below I focus on the excitation energies, AE, of the Be states that are discussed here. The nice thing about atomic spectra of this type is that there is accurate experimental information with which one can compare the results of a theoretical method (See, Tables of NIST, USA, in the WWW). Specifically, I compare the AE from the Be Fermi-sea energies for which cancellations on subtraction of total energies are expected, with those obtained from methods that have used one of the known basis sets. I consider two such publications. The first is in 1986 by Graham et al. [105] where a (9s9p5d) contracted GTO basis (61 basis functions) was used for different types of computations. I keep the full Cl (FCI) results. The second is in 2003 by Sears, Sherrill and Krylov [106], who studied aspects of "spin-flip" methods and compared them with FCI using the same basis set, which is a 6-31G. 

A recently introduced method called SWIFT (SWeep Imaging with Fourier Transform) is a fundamentally different approach to MRI which is particularly well suited to imaging objects with extremely fast spin-spin relaxation rates." The method exploits a frequency-swept excitation pulse and virtually simultaneous signal acquisition in a time-shared mode. The experimental steps needed to properly implement HSn pulses in SWIFT and compact expressions are presented to estimate the amplitude and flip angle of the HSn pulses, as well as the relative energy deposited by the SWIFT sequence. 

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