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Recursion formulas for nonlinear density fluctuations near the glass transition

The time-convolutionless mode-coupling (TMCT) equation for the intermediate scattering function $f_α(q,t)$ derived recently by the present author is transformed into a simple nonlinear recursion formula for a generating function $Ω_α(\bm{q},t)(=-\ln[f_α(q,t)]/q^2)$, where $α=c$ stands for a collective case and $α=s$ for a self case. By employing the same simplification on the nonlinear memory function as that proposed by the mode-coupling theory (MCT), the simplified asymptotic recursion formula is then derived and is numerically analyzed for different temperatures under the initial conditions obtained from the simulation. In a liquid state the numerical results are shown to recover the simulation results well. Although they can describe the simulation results well in the $β$-relaxation stage even for lower temperatures, they do not agree with those in the so-called $α$-relaxation stage because of the simplified model. The coupling parameter $λ^{(α)}$ dependence of the Debye-Waller factor $f_α$ is also discussed. The critical point is found as $λ_c^{(c)}=2e(\simeq 5.43656)$ and $f_c=e^{-1/2}(\simeq 0.60653)$, while MCT gives $λ_c^{(c)}=4.0$ and $f_c=1/2$. Then, the critical temperature $T_c$ is shown to be definitely lower than that predicted by MCT. Thus, it is emphasized that the present theory can improve the high $T_c$ problem appeared in MCT. The time evolution of the memory function and that of the diffusion coefficient are also investigated within asymptotic formulas.