What Parameter Should Be Used in Variational Approximation for This Hamiltonian?

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Hello. I should find the energy aproximatelly using the variational approximation for this physical hamiltonian: ##bx^4 + p²/2m## Imediatally, i thought that the better trial wave function would be the one correspondent to the ground state of the harmonic quantum oscilator. THe problem is, in fact, that i don't know what parameter to use in order to vary it! I mean, $$\psi = (mw/\pi \hbar)^{1/4}e^{-mwx^2/2 \hbar}$$. So, what parameter should i use? w=w(\alpha)? or m = m(\alpha)? How do i know by the beginning what parameter should i use to vary it?
 
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