1. A method of calculating an electronic state of a material by using a calculation device, the method comprising: setting a set containing, as elements, a plurality of operation models loaded in a memory of the calculation device by using the calculation device, where each of the operation models provides an approximate solution to an exact solution of the electronic state of the material; determining, in order to specify all of the operation models, for each operation model, an effective Hamiltonian including effective interactions that act on an electron system containing two or more electrons existing on a plurality of electron orbitals, by using the calculation device; determining, in a process of calculating a self-consistent solution of the effective Hamiltonian by using each of the operation models in the set, an optimized operation model among a plurality of operation models that are close in distance in a space obtained by introducing a distance to the set through a use of an absolute norm between electronic densities given by the operation models, based on a quantum mechanical variational method while defining a direction in which the calculated self-consistent solutions continuously change by using the calculation device; evaluating, when the optimized operation model is successively updated, a variational energy of the electron system by the self-consistent solution of the effective Hamiltonian by using the calculation device; updating the optimized operation model by using the calculation device so that the evaluated variational energy approaches an energy of the exact solution to be calculated and further, so that the variational energy forms a monotonically decreasing convex function; calculating the exact solution of the electronic state from one or a plurality of variational energy series by using the calculation device, and executing an operation of storing the calculated exact solution or a series of the variational energy that approaches the exact solution in the memory by using the calculation device; wherein among one or a plurality of series of the operation models that provide a series of the variational energy that approaches the exact solution, the series that includes the following operation model is determined by the calculation device, wherein the operation model provides a quantum phase shown by the electronic state, the quantum phase is equated with the exact solution without occurring a phase transition, and the operation model attains the self-consistent solution of the effective Hamiltonian by a minimum number of calculation steps, and wherein all of the operation models which are contained in the set are defined to be those satisfying following conditions (i) to (v), (i) the operation models obey a variational principle of a quantum mechanics, (ii) the series of the operation models is a coverging series with respect to a primary order parameter of the electron system, where the primary order parameter is electron density, (iii) the series has no phase transition point among the operation models in the series, (iv) each of the operation models has a continuous modification path connecting to an exact quantum mechanical representation of the material, (v) without the phase transition point, each of the operation models connects to a higher-ranked model series where a lambda-modification path defined by subtraction of a positive-definite functional from the exact quantum mechanical representation exists.