Operator error estimates for homogenization of the nonstationary Schrödinger-type equations: sharpness of the results

Abstract: In $L_2 (\mathbb{R}^d; \mathbb{C}^n)$, we consider a selfadjoint matrix strongly elliptic second order differential operator $\mathcal{A}\varepsilon$ with periodic coefficients depending on $\mathbf{x}/\varepsilon$. We find approximations of the exponential $e^{-i \tau \mathcal{A}\varepsilon}$, $\tau \in \mathbb{R}$, for small $\varepsilon$ in the ($H^s \to L_2$)-operator norm with suitable $s$. The sharpness of the error estimates with respect to $\tau$ is discussed. The results are applied to study the behavior of the solution $\mathbf{u}\varepsilon$ of the Cauchy problem for the Schr\"{o}dinger-type equation $i\partial{\tau} \mathbf{u}\varepsilon = \mathcal{A}\varepsilon \mathbf{u}_\varepsilon + \mathbf{F}$.