Due to rapid developments in laser spectroscopy and laser cooling and trapping techniques, atomic transition frequencies and other properties can now be measured to an unprecedented precision. These experimental advances provide many excellent opportunities for theorists to test existing theories and to explore new physics. The challenge to theorists is to perform high-precision calculations for various small but extremely important contributions arising from relativistic and quantum electrodynamic (QED) effects.
Few-body atomic and molecular systems, such as He, Li, PsH, H2+, H2 hold a special place in our understanding of microscopic world. From a structure point of view they are simple: three and four body systems, they are, however, intrinsically complex and contain physics (this is true even for the atomic hydrogen, the simplest atom, if one explores relativistic and QED effects). For these systems, an additional challenge to theorists is that the Schrodinger equation can not be solved exactly even in the nonrelativistic limit, due to the existence of Coulomb correlations. Thus, in order to match or even exceed modern spectroscopic accuracy, novel approximation methods need to be invented. New variational methods developed recently by us have shown a great promise of obtaining precise solutions to the Schrodinger equation for a general three or four body system. For example, the ground state energy of Li has now been calculated to an accuracy of a few parts in 1012. The key to the success is the explicit inclusion of interelectronic distances in our variational basis sets, which is particularly powerful in handling complex correlation effects between electrons. With these very precise wavefunctions, relativistic and QED effects can be treated perturbatively. The significance of these calculations is that they have set a new standard of accuracy, and they have stimulated several experimental groups, including Harvard (Gabrielse), NIST (Sansonetti), Florence (Inguscio), GSI at Darmstadt (Dax), York University (Hessels), Florida State University (Myers), and University of Northern Texas (Shiner) to perform high precision measurements for comparison.
W. Nortershauser, et al. Nuclear charge radii of 7,9,10Be and the one-neutron halo nucleus 11Be, Phys. Rev. Lett. (in press) (2009).
Z.-C. Yan, W. Nortershauser, and G. W. F. Drake, High precision atomic theory for Li and Be+: QED shifts and isotope shifts, Phys. Rev. Lett. vol. 100, 243002 (2008).
Z.-C. Yan and Y. K. Ho, Resonances with unnatural parities in the positron-hydrogen system Phys. Rev. A vol. 77, 030701 (Rapid Communication) (2008).
G. W. F. Drake and Z.-C. Yan, Studies of light halo nuclei from atomic isotope shifts, in Advances in Quantum Chemistry, vol. 53, 37 (2008).
H. Li, J. Wu, B.-L. Zhou, J.-M. Zhu, and Z.-C. Yan, Calculations of energies of the hydrogen molecular ion, Phys. Rev. A vol. 75, 012504 (2007).
R. Sanchez, et al, Nuclear Charge Radii of 9,11Li: The Influence of Halo Neutrons, Phys. Rev. Lett. vol. 96, 033002 (2006).
J.-Y. Zhang, Z.-C. Yan, D. Vrinceanu, J. F. Babb, and H. R. Sadeghpour, Long-range interactions between a He(23S) atom and a He(23P) atom for like isotopes, Phys. Rev. A vol. 73, 022710 (2006).
G. W. F. Drake, W. Nortershauser, and Z.-C. Yan, Isotope Shifts and Nuclear Radius Measurements for Helium and Lithium, Can. J. Phys. vol. 83, 311 (2005).
J.-Y. Zhang, Z.-C. Yan, D. Vrinceanu, and H. R. Sadeghpour, Anisotropic van der Waals coefficients for He(11S) and He(23P), Phys. Rev. A vol. 71, 032712 (2005).
G. Ewald, et al, Nuclear Charge Radii of 8,9Li Determined by Laser Spectroscopy, Phys. Rev. Lett. vol. 93, 113002 (2004).
Y. K. Ho and Z.-C. Yan, High partial wave resonances in positron hydrogen scattering, Phys. Rev. A vol. 70, 032716 (2004).
Z.-C. Yan and G. W. F. Drake, Bethe logarithm and QED shift for lithium, Phys. Rev. Lett. vol. 91, 113004 (2003).
Z.-C. Yan and J.-Y. Zhang, “Energies of the hydrogen molecular ions in high-angular-momentum states”, Journal of Physics B , Vol. 37, 1055 (2004).
J.-Y. Zhang and Z.-C. Yan, “Long-range interactions for hydrogen molecular ions”, Journal of Physics B, Vol. 37, 723 (2004).
Z.-C. Yan and G. W. F. Drake, “Bethe logarithm and QED shift for lithium”, Physical Review Letters, Vol. 91, 113004 (2003).
Z.-C. Yan and Y. K. Ho, “Determination of resonance energies and widths in Ps-H scattering using the stabilization method”, Journal of Physics B, Vol. 36, 4417 (2003).
Y. K. Ho and Z.-C. Yan, “High-angular-momentum resonances in positron scattering by He+ ion”, Physical Review A, Vol. 66, 062705 (2002).
Z.-C. Yan, "Polarizabilities and dispersion coefficients of positronium hydride", Journal of Physics B, Vol. 35 L345 (2002).
Z.-C. Yan, "Calculations of Magnetic Moments for Three-Electron Atomic systems", Physical Review Letters, Vol. 86, 5683 (2001).
Z.-C. Yan and G. W. F. Drake, "Lithium isotope shifts as a measure of nuclear size", Physical Review A 61, 022504 (2000).
Z.-C. Yan, "Double photoionization of Li and Be+ at high-energy limit", Physical Review A 60 (Rapid Commun), 3358 (1999).
Z.-C. Yan and G. W. F. Drake, "Relativistic and QED energies in lithium", Physical Review Letters Vol. 81, 774-777 (1998).
Z.-C. Yan and G. W. F. Drake, "Lithium fine structure in the 1s1s2p 2PJ states", Physical Review Letters Vol. 79, 1646-1649 (1997).
Z.-C. Yan and G. W. F. Drake, "High Precision Calculation of Fine Structure Splittingin Helium and He-like Ions", Physical Review Letters Vol. 74, 4791-4794 (1995).
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