Hello,

I am trying to build a SiO2 surface grafted with hydroxyl groups. I first import the quartz structure, cleaved it along (001) plane. Then I added hydrogen bonded with oxygen. After that, I calculated the forcefield parameters using COMPASS. However, comparing with a literature, the charges of the atoms are very different. For example, the H atoms had charges of 0.35, while in my structure, the charges of H atoms are 0.25. The O atoms are -0.76, and the Si atoms are 1.73, while mine are -0.4725 and 0.89, respectively. Does anyone know the why? Thank you very much! The figures of SiO2 with hydroxyl are attached here. The first one is what I built. The second one is from the literature.