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IntechOpen eBooks

On the Generalized Quantum Linear Momentum Operator

Jesús García‐Ravelo, Jesús García-Martínez, Jesús Morales, José Juan Peña

Published Feb 11, 2025• 0 citations
Publisher

Abstract

From the canonical form of the position-dependent mass Hamiltonian, the generalized quantum linear momentum operator (GLMO) is obtained. Such operator is straightforwardly generated by rewritten the Schrödinger Hamiltonian in terms of von Ross kinetic energy operator, expressed as the square of the Hermitian GLMO plus a potential energy function. In this scheme, the hermiticity property and the arbitrary ambiguity parameters remain in force. In addition, by means of different methods, it is shown that the GLMO has a unique structure regardless of the form of the mass distribution. Hence, the proposed approach is valid for any physically plausible position-dependent mass distribution mx. As an example of useful applications of our proposal, two specific mx with arbitrary ambiguity parameters are considered. The application is given for some potential models, such as the null potential, the harmonic oscillator, the double well potential, and the Coulomb-like potential. For some particular values of the ambiguity parameters, our results agree with some already published in the literature, which means that our method can be considered as an improvement vis-a-vis those proposals on the same subject given until now.

DOI
10.5772/intechopen.1009028

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From the canonical form of the position-dependent mass Hamiltonian, the generalized quantum linear momentum operator (GLMO) is obtained. Such operator is straightforwardly generated by rewritten the Schrödinger Hamiltonian in terms of von Ross kinetic energy operator, expressed as the square of the Hermitian GLMO plus a potential energy function. In this scheme, the hermiticity property and the arbitrary ambiguity parameters remain in force. In addition, by means of different methods, it is shown that the GLMO has a unique structure regardless of the form of the mass distribution. Hence, the proposed approach is valid for any physically plausible position-dependent mass distribution mx. As an example of useful applications of our proposal, two specific mx with arbitrary ambiguity parameters are considered. The application is given for some potential models, such as the null potential, the harmonic oscillator, the double well potential, and the Coulomb-like potential. For some particular values of the ambiguity parameters, our results agree with some already published in the literature, which means that our method can be considered as an improvement vis-a-vis those proposals on the same subject given until now.
In this work, the quantum operator approach is applied to both, the position-dependent mass Schrödinger equation (PDMSE) and the Schrodinger equation with constant mass (CMSE). This fact enable us to find the factorization operators that relates both Hamiltonians by means of a kinetic energy operator that comes from the proposal of Morrow and Brownstein. With this approach is possible to find the exactly-solvable PDMSE, for any value of the parameters α and γ in the von Roos's Hamiltonian. For that, our proposal can be considered as a unified treatment of the PDMSE because it contains as particular cases, the kinetic energy operators of various authors such as BenDaniel-Duke, Gora-Williams, Zhu-Kroemer and Li-Kuhn among others. To show the usefulness of our result, we show the solvable PDMSE that comes from the harmonic oscillator potential model for the CMSE. The proposal is general and can easily be extended to other potential models and mass distributions which will be given in the extended paper.
The von Roos’ position dependent mass Schrödinger Equation (PDMSE) is given in terms of an effective potential, which is constructed by the potential under study and additional terms involving the position dependent mass and the ambiguity ordering parameters. At this regard, some of the most important approaches to the ambiguity parameters are those of BenDaniel-Duke, Gora-Williams, Zhu-Kroemer, Li-Kuhn and so on. In this work we show that for the cases of Zhu-Kroemer and BenDaniel-Duke it is possible to express any solvable potential through a couple of quantum superpotentials. For this, we stablish the factorization of the PDMSE Hamiltonian and the use of a point canonical transformation; these allow to identify a first superpotential W(x). Next, the term in the effective potential with ambiguity parameters is expressed through a function Z(x) and later the cases when Z(x) is a quantum superpotential are discussed. This way, the proposed superpotentials determine the solvable potentials in the PDMSE, the energy spectra and mass functions. We give some examples to explain the approach which can be straightforwardly applied to the solution of the PDMSE for other different potential models and mass distributions.
Abstract The exactly solvable Position Dependent Mass Schrödinger Equation (PDMSE) for Mie-type potentials is presented. To that, by means of a point canonical transformation the exactly solvable constant mass Schrödinger equation is transformed into a PDMSE. The mapping between both Schrödinger equations lets obtain the energy spectra and wave functions for the potential under study. This happens for any selection of the O von Roos ambiguity parameters involved in the kinetic energy operator. The exactly solvable multiparameter exponential-type potential for the constant mass Schrödinger equation constitutes the reference problem allowing to solve the PDMSE for Mie potentials and mass functions of the form given by m(x) = skx s-1/(xs + 1))2. Thereby, as a useful application of our proposal, the particular Lennard-Jones potential is presented as an example of Mie potential by considering the mass distribution m(x) = 6kx 5/(x 6 + 1))2. The proposed method is general and can be straightforwardly applied to the solution of the PDMSE for other potential models and/or with different position-dependent mass distributions.
We consider the problem of removal of ordering ambiguity in position dependent mass quantum systems characterized by a generalized position dependent mass Hamiltonian which generalizes a number of Hermitian as well as non-Hermitian ordered forms of the Hamiltonian. We implement point canonical transformation method to map one-dimensional time-independent position dependent mass Schrödinger equation endowed with potentials onto constant mass counterparts which are considered to be exactly solvable. We observe that a class of mass functions and the corresponding potentials give rise to solutions that do not depend on any particular ordering, leading to the removal of ambiguity in it. In this case, it is imperative that the ordering is Hermitian. For non-Hermitian ordering, we show that the class of systems can also be exactly solvable and is also shown to be iso-spectral using suitable similarity transformations. We also discuss the normalization of the eigenfunctions obtained from both Hermitian and non-Hermitian orderings. We illustrate the technique with the quadratic Liénard type nonlinear oscillators, which admit position dependent mass Hamiltonians.
The position-dependent mass Schrodinger equation (PDMSE) comes from the O von Roos quantum Hamiltonian which models to position-dependent effective mass quantum systems. The algebraic study of its factorization is compared in this work with the factorization of the traditional constant mass Schrödinger equation so that both equations are related by similarity transformations. The approach allows building solvable cases of the PDMSE for any value of the ambiguity parameters in the general Hamiltonian of O von Roos, so it can be considered as a unified treatment of the PDMSE that contains as particular cases those Hamiltonians of various authors such as BenDaniel-Duke, Gora-Williams, Zhu-Kroemer and Li- Kuhn, among others. We explicitly show the PDMSE solutions coming from the harmonic, Morse and multiparameter exponential-type potentials. The method is general and can be easily extended to other potential models and position dependent mass distributions useful in the mathematical modeling of quantum systems.
We solve the parametric generalized effective Schrödinger equation with a specific choice of position-dependent mass function and Morse oscillator potential by means of the Nikiforov–Uvarov method combined with the Pekeris approximation scheme. All bound-state energies are found explicitly and all corresponding radial wave functions are built analytically. We choose the Weyl or Li and Kuhn ordering for the ambiguity parameters in our numerical work to calculate the energy spectrum for a few (H2, LiH, HCl and CO) diatomic molecules with arbitrary vibration n and rotation l quantum numbers and different position-dependent mass functions. Two special cases including the constant mass and the vibration s-wave (l = 0) are also investigated.