# A question about physical chemistry

Please post this type of questions in HW section using the template.
For the problem of particle in a 1D box
V(x)=0 for 0≦x≦a
∞ for anywhere outside the box
I know that Hamiltonian operator commutes with momentum operator
so they should have smae eigenfunction but it's obvious that the wavefunction
(2/a)^1/2sin(nπx/a) is not a eigenfunction of linear momentum operator
what is the reason for the contradiction ?

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