We present a modeling platform that combines atomic scale ab-initio simulations and TCAD device simulations to evaluate new gate stack materials for gate-all-around (GAA) devices. Advanced technology nodes currently employ high-K metal gate (HKMG) technology to enhance FinFET transistor performance while mitigating gate leakage current. This is accomplished with a combination of work function metals (WFM), high-K dielectric and work-function tuning to maintain equivalent oxide thickness and gate electrostatics as devices are scaled. As a result, HKMG-based FinFET devices can be tuned for various design requirements from super-low threshold voltages (SLVT) to (HVT). For advanced technology nodes N3 and beyond, FinFET devices are expected to be supplanted by GAA devices due to improved gate electrostatics. However, the restricted space around GAA silicon nanosheets poses significant challenges to implement the current FinFET technology gate stack. The introduction of dipole materials, with an electron affinity different from the high-K oxide, offers the possibility for variable threshold voltages without work-function metals, while maintaining EOT and gate electrostatics. This offers a greatly simplified gate stack process for advanced node GAA devices. Ab-initio simulations can be vital in discovering these novel dipole materials and elucidating the mechanism of dipole field generation. In this work, we initially develop atomic scale structures of HKMG material stack including a dipole material with thickness ranging from 2.5 to 10 Angstrom. The dipole materials used are AlOx for p-type WF shift and LaOx for n-type WF shift. Ab-initio simulations are conducted to predict the shifts caused in the effective work-function of the HKMG stack by the introduction of the dipole layer. In second simulation step, we used the obtained threshold values from work-function shifts in the TCAD device simulations. We showed how VT shifts with varying dipoles from ab-initio scale can be correlated with device performance regardless of the nanosheet spacing.