OPTICAL-LINE SHAPES OF INHOMOGENEOUSLY BROADENED EXCITON-TRANSITIONS IN THE COHERENT POTENTIAL APPROXIMATION

We have carried out a series of calculations of the optical line shapes of inhomogeneously broadened excition transitions within the framework of the coherent potential approximation (CPA). A Gaussian distribution of transition frequencies was assumed. In this paper, we present detailed results for Frenkel excitons in simple cubic systems with nearest-neighbor interactions. The theoretical predictions are compared with numerical simulations. Good agreement is obtained over a wide range of the ratio of the width of the distribution of transition frequencies to the exciton bandwidth. Previous limitations attributed to the CPA are shown to result from inaccuracies in the numerical evaluation of Green's function or in the treatment of the Gaussian averaging.