Ground-state properties of EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ by many-variable variational Monte Carlo method

The organic Mott insulator EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ is a strongly correlated electron system on a nearly-regular triangular lattice and regarded as a spin liquid material. We investigate its effective low-energy model derived from first principles calculations and band+dimensional downfolding. The {\it ab initio} effective Hamiltonian is given in the form of the two-dimensional single-band extended Hubbard model on an anisotropic triangular lattice with short-ranged Coulomb and exchange interactions. Its ground state is calculated by the many-variable variational Monte Carlo method with quantum-number projection and multi-variable optimization. We draw the ground-state phase diagram as a function of scaling parameters for the interactions and the geometrical frustration by extending the {\it ab initio} model. We discuss Mott transitions and magnetic properties.