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To find a well-motivated energy density, we start from a possibly fundamental, relativistic description for a spin-<mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mfrac><mml:mn>1<\/mml:mn><mml:mn>2<\/mml:mn><\/mml:mfrac><\/mml:math> particle: Dirac's equation. Employing its energy-momentum tensor and going to the non-relativistic limit we find a locally conserved non-relativistic energy density that is defined via the Terletsky-Margenau-Hill quasiprobability (which is hence selected among other options). It coincides with the weak value of energy, and also with the hydrodynamic energy in the Madelung representation of quantum dynamics, which includes the quantum potential. Moreover, we find a new form of spin-related energy that is finite in the non-relativistic limit, emerges from the rest energy, and is (separately) locally conserved, though it does not contribute to the global energy budget. This form of energy has a holographic character, i.e., its value for a given volume is expressed via the surface of this volume. Our results apply to situations where local energy representation is essential; e.g. we show that the energy transfer velocity for a large class of free wave-packets (including Gaussian and Airy wave-packets) is larger than its group (i.e. coordinate-transfer) velocity.<\/jats:p>","DOI":"10.22331\/q-2024-01-10-1223","type":"journal-article","created":{"date-parts":[[2024,1,10]],"date-time":"2024-01-10T14:45:15Z","timestamp":1704897915000},"page":"1223","update-policy":"http:\/\/dx.doi.org\/10.22331\/q-crossmark-policy-page","source":"Crossref","is-referenced-by-count":1,"title":["Energy densities in quantum mechanics"],"prefix":"10.22331","volume":"8","author":[{"given":"V.","family":"Stepanyan","sequence":"first","affiliation":[{"name":"Institute of Physics, Yerevan State University, 0025 Yerevan, ArmeniaAlikhanian National Laboratory, 0036 Yerevan, Armenia"}]},{"given":"A.E.","family":"Allahverdyan","sequence":"additional","affiliation":[{"name":"Institute of Physics, Yerevan State University, 0025 Yerevan, ArmeniaAlikhanian National Laboratory, 0036 Yerevan, Armenia"},{"name":"Energy densities in quantum mechanics"}]}],"member":"9598","published-online":{"date-parts":[[2024,1,10]]},"reference":[{"key":"0","unstructured":"L. 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