Using the eective mass treatment of the low-energy valleys of Si nanodevices in conjunction with a highly adaptable TCO emulation of the articial gate connement in a Si DQD qubit, we have introduced an appropriate single-particle set of space orbitals, which, when augmented through multiplication with the spin and isospin up and down functions, are used as the input of spinisospin-orbitals in the construction of the many-body CI basis of Slater determinants (Sec. III).