= Cubic-term removal in a conserved quartic Landau free energy
{title2=$\phi=\psi-c/(3b)$}
For a scalar <Landau free energy> $f=a\phi^2/2+b\phi^4/4+c\phi^3/3+d\phi$ with $b>0$, the shift $\phi=\psi-c/(3b)$ removes the cubic term. The quadratic coefficient becomes $a'=a-c^2/(3b)$ and the linear coefficient becomes $d'=d-ac/(3b)+2c^3/(27b^2)$. In a closed <binary fluid mixture>, the linear term is constant at fixed total composition, leaving the symmetric quartic <phase coexistence> construction in the shifted variable.
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