The problem of application of Gaussian and non-Gaussian basic measure densities of collective variables for integration a cluster ferroelectric partition function functional is discussed. Starting from the conver- gence of functional integrals in the phase transition point vicinity the first Brillouin zone is divided into layers. Every layer consists of two parts. In the first one the Gaussian measure density is sufficient and in the second one the non-Gaussian measure density must be used. The partition function obtained as a result of layer by layer integration is finite in the temperature region which contains the neighbourhood of phase transition point. The critical behaviour of a thermodynamic functions is studied.