<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>5</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Sihong Shao</style></author><author><style face="normal" font="default" size="100%">Zhendong Li</style></author><author><style face="normal" font="default" size="100%">Wenjian Liu</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Coalescence Conditions of Relativistic Wave Functions</style></title><secondary-title><style face="normal" font="default" size="100%">Handbook of Relativistic Quantum Chemistry</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2017</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://link.springer.com/referenceworkentry/10.1007/978-3-642-41611-8_8-1</style></url></web-urls></urls><publisher><style face="normal" font="default" size="100%">Springer</style></publisher><pub-location><style face="normal" font="default" size="100%">Berlin</style></pub-location><pages><style face="normal" font="default" size="100%">497-530</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The electron-electron coalescence conditions for the wave functions of the Dirac-Coulomb&amp;nbsp;(DC), Dirac-Coulomb-Gaunt (DCG), and Dirac-Coulomb-Breit (DCB) Hamiltonians are analyzed by making use of the internal&amp;nbsp;symmetries of the reduced two-electron systems. The&amp;nbsp;results show that, at the coalescence point of two electrons, the&amp;nbsp;wave functions of the DCG Hamiltonian are regular, while those of&amp;nbsp;the DC and DCB Hamiltonians have $r_{12}^{\nu}$ type weak singularities,&amp;nbsp;with $\nu$ being negative and of $\mathcal{O}(\alpha^2)$. Yet, such&amp;nbsp;asymptotic expansions of the relativistic wave functions are only valid within an extremely small convergence radius $R_c$ of&amp;nbsp;$\mathcal{O}(\alpha^2)$. Beyond this radius, the behaviors of the&amp;nbsp;relativistic wave functions are still dominated by the&amp;nbsp;nonrelativistic limit.&amp;nbsp;</style></abstract></record></records></xml>