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Existence criteria

The existence of a bound state is guaranteed if any of the existence criteria are met.

By variational Method

By variational method of finding ground state, if there exists a trial wavefunction whose energy expectation value is negative, there exists ground state solution which is bounded.[1]

Bound states of Attractive potential

It can be shown that attractive potentials with negative spacial integral have at least one bound states in the dimensions .[2] Since this means that the potential has to go to zero to give a non-divergent integral, the potential is offset by it's values at infinity and the condition expressed as:

Node theorem

Node theorem states that n-th bound wavefunction ordered according to increasing energy has exactly n-1 nodes, ie. points where . Rigorous derivation of the condition is treated in analysis of second order homogenous differential equations.

Due to the form of Schrodinger's time independent equations, it is not possible for a physical wavefunction to have since it corresponds to solution by the uniqueness of second order ordinary differential solutions. Considering a rigid wall around a point with , if the walls expand to infinity, , the eigenfunctions of the trapped system morphs into eigenfunctions of the Hamiltonian. If the new nodes are formed during this, then at some value of and point within the walls, either the nodes begin to form at the middle with or at the boundaries with or . Since wavefunction always remains zero at rigid walls, condition ensures that nodes are not formed and that the sign of these derivatives remain the same. At the instant the node begins to form at , it will be a local minima and hence have which is not possible.[3]


As a corollary, the no-node theorem states that the ground state of bound particles do not have any nodes.

References

Methods of Mathematical Physics Vol. I - Courant and Hilbert pp 451-455

https://arxiv.org/pdf/quant-ph/0702260.pdf

See Also

Sturm–Picone comparison theorem

Sturm separation theorem

  1. ^ "Criterion for existence of a bound state in one dimension". pubs.aip.org. doi:10.1119/1.19389. Retrieved 2023-12-14.
  2. ^ "titel".
  3. ^ Moriconi, M. (2007-03-01). "Nodes of wavefunctions". American Journal of Physics. 75 (3): 284–285. doi:10.1119/1.2404960. ISSN 0002-9505.

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