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In page Atomic orbital:

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Real spherical harmonics are physically relevant when an atom is embedded in a crystalline solid, in which case there are multiple preferred symmetry axes but no single preferred direction.[citation needed] Real atomic orbitals are also more frequently encountered in introductory chemistry textbooks and shown in common orbital visualizations.[2] In real hydrogen-like orbitals, quantum numbers n and have the same interpretation and significance as their complex counterparts, but m is no longer a good quantum number (but its absolute value is).