Hydrogen/silicon complexes in silicon from computational searches

Defects in crystalline silicon consisting of a silicon self-interstitial atom and one, two, three, or four hydrogen atoms are studied within density-functional theory (DFT). We search for low-energy defects by starting from an ensemble of structures in which the atomic positions in the defect region have been randomized. We then relax each structure to a minimum in the energy. We find a new defect consisting of a self-interstitial and one hydrogen atom (denoted by ${I,\text{H}}$) which has a higher symmetry and a lower energy than previously reported structures. We recover the ${I,{\text{H}}_{2}}$ defect found in previous studies and confirm that it is the most stable such defect. Our best ${I,{\text{H}}_{3}}$ defect has a slightly different structure and lower energy than the one previously reported, and our lowest-energy ${I,{\text{H}}_{4}}$ defect is different to those of previous studies.