Due to its extreme sensitivity to a number of factors such as lattice mismatch, defect accumulation, interfacial bond formation, and dipoles formation, effective work function (EWF) of metal gate for metal-oxide-semiconductor field-effect transistor (MOSFET) could differ from its vacuum work function1-3.Thus, achieving a suitable gate metal is still a challenge.Using first-principle calculation, we studied two systems as follows: (1) the effects of two strain modes (uniaxial and triaxial strains) on the EWF of Hf-Ni and O-Ni interfaces that HfO2 terminated with Hf atom and O atom respectively for Ni(001)/HfO2(001) interfaces without interfacial defects.The calculated results indicate that the EWFs for two interfaces are strongly affected by the type of interface and the strain modes.For both strain modes, the variation of EWF linearly increases as the strain increases, but for a certain strain, the variation of EWF for triaxial strain is larger than that for uniaxial strain.Moreover, the electrons gas model, interface dipole and screening role of HfO2 were used to analyze and explain strain and interface effects in metal-oxide interfaces.This work strongly suggests that controlling the strain and interface structure is a promising way for modulating the EWF of Ni/HfO2 interfaces;(2) The effects of point defects on the EWF for Hf-Ni and O-Ni interfaces.The calculated results indicate that the EWF strongly depends on interface roughness and interfacial own atom substitution without bringing extrinsic contaminant.For Hf-Ni interface, two calculated work functions of the two interfaces without Ni substitution and with Ni substitution for whole interfacial Hf layer were good for nMOS and pMOS effective work function (EWF) engineering.The EWFs were sensitive to Hf vacancy rather than Ni vacancy in interfacial layer.And for O-Ni interface, oxygen vacancies result in a decrease in work function.We also basically acquire an expected theoretical relationship that variations of the EWFs are in proportion to that of interface dipole density.Atomic electronegativity and interface dipole were used to analyze and explain the effects of interfacial point defects on the EWE This work strongly suggests that controlling interfacial own atom substitution and interface roughness are very attractive and promising ways for modulating the EWF of Ni/HfO2 interfaces.