Ab-initio Methods for Quantum Calculations on Surface Energies

• Main Authors: Hsiao-Wei Chang, 張孝維
• Other Authors: 劉柏良
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/55674910084990070330

碩士 === 國立中興大學 === 精密工程學系所 === 100 === We conduct ab-initio calculations to estimate the convergence of the surface energies for Ge(001) thin films and the cleavage energies for GaN(0001)/(000-1) thin films by using the bulk-energy approach, incremental energy approach, energy fit approach and vacuum approach. The surface energy of Ge(001) thin films is 0.086 eV/Å2 calculated from the energy fit approach. The surface energies of Ge(001) thin films calculated from the bulk-energy approach diverge with increasing the slab thickness. The surface energies of Ge(001) thin films calculated from the incremental energy approach converge with increasing the slab thickness. The surface energies of Ge(001) thin films calculated from the vacuum approach are consistent with the convergent value of 0.086 eV/Å2, which the vacuum thickness is 5.77Å(0.25 times larger than slab thickness). We find that both the surface energies of Ge(001) thin films calculated from incremental energy approach and from vacuum approach are identical to the value of 0.086 eV/Å2, which is estimated from energy fit approach. The cleavage energy of GaN(0001)/(000-1) thin films is 0.363 eV/Å2 calculated from the energy fit approach. The cleavage energies of GaN(0001)/(000-1) thin films from the bulk-energy approach converge with increasing slab thickness. The cleavage energies of GaN(0001)/(000-1) thin films from the incremental energy approach converge with increasing slab thickness. The cleavage energies of GaN(0001)/(000-1) thin films calculated from vacuum approach are close to the convergent value, which the vacuum thickness is 5.24Å(0.5 times larger than slab thickness). The converged cleavage energies of GaN(0001)/(000-1) thin films calculated from the bulk-energy approach, incremental energy approach and vacuum approach are 0.370 eV/Å2, 0.368 eV/Å2 and 0.369 eV/Å2, respectively. Both the energy fit approach and the vacuum approach are suitable for estimating the surface energy of Ge(001) thin films and the cleavage energies of GaN(0001)/(000-1) thin films. The advantage of vacuum approach is few computational cost of the accuracy surface/cleavage energies for Ge(001) thin films and GaN(0001)/(000-1) thin films.