Abstract
Given the Thomas–Fermi equation \(\sqrt{x}\varphi ''=\varphi ^{3 \over 2}\), this paper changes first the dependent variable by defining \(y(x) \equiv \sqrt{x \varphi (x)}\). The boundary conditions require that y(x) must vanish at the origin as \(\sqrt{x}\), whereas it has a fall-off behaviour at infinity proportional to the power \({1 \over 2}(1-\chi )\) of the independent variable x, \(\chi \) being a positive number. Such boundary conditions lead to a 1-parameter family of approximate solutions in the form \(\sqrt{x}\) times a ratio of finite linear combinations of integer and half-odd powers of x. If \(\chi \) is set equal to 3, in order to agree exactly with the asymptotic solution of Sommerfeld, explicit forms of the approximate solution are obtained for all values of x. They agree exactly with the Majorana solution at small x, and remain very close to the numerical solution for all values of x. Remarkably, without making any use of series, our approximate solutions achieve a smooth transition from small-x to large-x behaviour. Eventually, the generalized Thomas–Fermi equation that includes relativistic, non-extensive and thermal effects is studied, finding approximate solutions at small and large x for small or finite values of the physical parameters in this equation.
Similar content being viewed by others
Notes
If one looks for solutions of Eq. (1.2) in the form \(\varphi (x)=A x^{\alpha }\), one finds the consistency condition
$$\begin{aligned} {\alpha (\alpha -1)\over \sqrt{A}}=x^{(3+\alpha )\over 2}, \end{aligned}$$which implies that \(\alpha =-3\), and hence \({12 \over \sqrt{A}}=1\), which is solved by \(A=144\).
References
L.H. Thomas, The calculations of atomic fields. Proc. Cambridge Philos. Soc. 23, 542–598 (1927)
E. Fermi, Eine statistiche methode zur bestimmung einiger eigenschaften des atoms und ihre anwendung auf die theories des periodischen systems der elemente. Z. Phys. 48, 73–79 (1928)
S. Esposito, E. Majorana Jr., A. van der Merwe, E. Recami, Ettore Majorana: Notebooks in Theoretical Physics (Kluwer, Dordrecht, 2003)
E. Di Grezia, S. Esposito, Fermi, Majorana and the statistical model of atoms. Found. Phys. 34, 1431–1450 (2004)
S. Esposito, Majorana solution of the Thomas–Fermi equation. Am. J. Phys. 70, 852–856 (2002)
A. Sommerfeld, Integrazione asintotica dell’equazione differenziale di Thomas–Fermi. Rend. R. Accademia dei Lincei 15, 293–308 (1932)
J. Sanudo, A.F. Pacheco, Electrons in a box: Thomas–Fermi solution. Can. J. Phys. 84, 833–844 (2006)
R.J. Komlos, A. Rabinovitch, Thomas–Fermi model for quasi one-dimensional finite crystals. Phys. Lett. A 372, 6670–6676 (2008)
W. Wilcox, Thomas–Fermi statistical models of finite quark matter. Nucl. Phys. A 826, 49–73 (2009)
B.G. Englert, Semiclassical Theory of Atoms (Springer, Berlin, 1988)
E. Martinenko, B.K. Shamoggi, Thomas–Fermi model: nonextensive statistical mechanics approach. Phys. Rev. A 69, 52504 (2004)
A. Nagy, E. Romera, Maximum Rényi entropy and the generalized Thomas–Fermi model. Phys. Lett. A 373, 844–846 (2009)
K. Ourabah, M. Tribeche, The nonextensive Thomas–Fermi theory in an \(n\)-dimensional space. Phys. A 392, 4477–4480 (2013)
K. Ourabach, M. Tribeche, Relativistic formulation of the generalized nonextensive Thomas–Fermi model. Phys. A 393, 470–474 (2014)
H. Shababi, K. Ourabah, On the Thomas–Fermi model at the Planck scale. Phys. Lett. A 383, 1105–1109 (2019)
H. Shababi, K. Ourabah, Thomas–Fermi theory at the Planck scale: a relativistic approach. Ann. Phys. (N.Y.) 413, 168051 (2020)
M. Ghozanfari Mojamad, J. Ranjbar, Thomas–Fermi approximation in the phase transition of neutron star matter from \(beta\)-stable nuclear matter to quark matter. Ann. Phys. (N. Y.) 412, 168048 (2020)
S. Kumar Roy, S. Mukhopadhyay, J. Lahiri, D.N. Basu, Relativistic Thomas–Fermi equation of state for magnetized white dwarfs. Phys. Rev. D 100, 063008 (2019)
M. Ghazanfari Mojarrad, J. Ranjbar, Hybrid neutron stars in the Thomas–Fermi theory. Phys. Rev. C 100, 015804 (2019)
K. Pal, L.V. Sales, J. Wudka, Ultralight Thomas–Fermi dark matter. Phys. Rev. D 100, 083007 (2019)
Acknowledgements
The authors are grateful to the Dipartimento di Fisica “Ettore Pancini” of Federico II University for hospitality and support.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Esposito, G., Esposito, S. A new approach to the Thomas–Fermi boundary-value problem. Eur. Phys. J. Plus 135, 491 (2020). https://doi.org/10.1140/epjp/s13360-020-00507-4
Received:
Accepted:
Published:
DOI: https://doi.org/10.1140/epjp/s13360-020-00507-4