A new tight-binding molecular dynamics approach for Si-H systems is developed using the valence orbitale of Si and H for calculation of atomic forces. Previous tight-binding models are not able to describe formation energies of different charge states of H in c-Si and new physics is introduced in our model to describe both effects of charge transfer and varying atomic environments. The Si-H Model was developed by fitting to silane, and ensuring that the formation energies of different charge states of H in c-Si were correctly described. This new model also describes well vibrational properties of SiHn configurations, and the structural and electronic properties of a-Si:H Models. The new molecular dynamics utilizes quantum mechanical forces, incorporating important electronic effects, and is robust enough to simulate hundreds of atoms as would be needed in realistic a-Si:H systems.