Artykuły naukowe (WCh)
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Browsing Artykuły naukowe (WCh) by Subject "beryllium atom"
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Item Dipole and quadrupole polarizabilities and shielding factors of beryllium from exponentially correlated Gaussian functions(American Physical Society, 2001-12-14) Komasa, JacekDynamic dipole and quadrupole polarizabilities as well as shielding factors of the beryllium atom in the ground state were computed at real frequencies by using the variation-perturbation method. The zeroth- and the first-order wave functions were expanded in many-electron basis of exponentially correlated Gaussian functions. The 1600-term expansion of the unperturbed wave function yielded the ground-state energy accurate to 1 cm-1. The first-order wave functions were expanded in very large bases (4800 and 4400 terms). The nonlinear parameters of the first-order correction functions were optimized with respect to both the static and dynamic polarizabilities, and with respect to the excited-state energies. The procedure employed ensures a high accuracy of determination of dynamic properties in a wide range of frequencies and correct positions of the transition poles. Test calculations, performed on He and Li, confirmed the ability of this method to obtain the atomic properties with very high accuracy. The final values of the static properties of Be were 37.755 e2a02EH-1 and 300.96 e2a04EH-1 for the dipole and quadrupole polarizabilities, respectively, and 1.4769 for the quadrupole shielding factor. The convergence of the atomic properties with the size of the expansion of both the zeroth- and first-order functions was checked. Thanks to very high accuracy of the unperturbed wave function and the efficient method of construction of the first-order wave functions, the dynamic polarizability results presented in this work are of benchmark quality. As a by-product of this project, a set of the most accurate upper bounds to the energies of 1P and 1D states of Be was obtained.Item On the acceleration of the convergence of singular operators in Gaussian basis sets(AMERICAN INSTITUTE OF PHYSICS, 2005-05-08) Pachucki, Krzysztof; Cencek, Wojciech; Komasa, JacekGaussian type wave functions do not reproduce the interparticle cusps which result in a slow convergence of the expectation values of the operators involved in calculations of the relativistic and QED energy corrections. Methods correcting this deficiency are the main topic discussed in this paper. Benchmark expectation values of the singular operators for several few-electron systems are presented.Item Relativistic and QED Corrections for the Beryllium Atom(American Physical Society, 2004) Pachucki, Krzysztof; Komasa, JacekComplete relativistic and quantum electrodynamics corrections of order α2 Ry and α3 Ry are calculated for the ground state of the beryllium atom and its positive ion. A basis set of correlated Gaussian functions is used, with exponents optimized against nonrelativistic binding energies. The results for Bethe logarithms lnk0(Be)=5.750 34(3) and lnk0(Be+)=5.751 67(3) demonstrate the availability of high precision theoretical predictions for energy levels of the beryllium atom and light ions. Our recommended value of the ionization potential 75 192.514(80) cm-1 agrees with equally accurate available experimental values.