@inbook {26666,
	title = {Coalescence Conditions of Relativistic Wave Functions},
	booktitle = {Handbook of Relativistic Quantum Chemistry},
	year = {2017},
	pages = {497-530},
	publisher = {Springer},
	organization = {Springer},
	address = {Berlin},
	abstract = {The electron-electron coalescence conditions for the wave functions of the Dirac-Coulomb\&nbsp;(DC), Dirac-Coulomb-Gaunt (DCG), and Dirac-Coulomb-Breit (DCB) Hamiltonians are analyzed by making use of the internal\&nbsp;symmetries of the reduced two-electron systems. The\&nbsp;results show that, at the coalescence point of two electrons, the\&nbsp;wave functions of the DCG Hamiltonian are regular, while those of\&nbsp;the DC and DCB Hamiltonians have $r_{12}^{\nu}$ type weak singularities,\&nbsp;with $\nu$ being negative and of $\mathcal{O}(\alpha^2)$. Yet, such\&nbsp;asymptotic expansions of the relativistic wave functions are only valid within an extremely small convergence radius $R_c$ of\&nbsp;$\mathcal{O}(\alpha^2)$. Beyond this radius, the behaviors of the\&nbsp;relativistic wave functions are still dominated by the\&nbsp;nonrelativistic limit.\&nbsp;},
	url = {https://link.springer.com/referenceworkentry/10.1007/978-3-642-41611-8_8-1},
	author = {Sihong Shao and Zhendong Li and Wenjian Liu}
}
