Session C16 - Computational Condensed Matter Physics.
MIXED session, Monday afternoon, March 20
205C, MCC

14:30
C16.01 Fast million atom pseudopotential calculations using SLCBB method
Lin-Wang Wang (NERSC, Lawrence Berkeley National Laboratory, Berkeley, California 94720)

k.p method has been used in the last thirty years to calculate the electronic structures of semiconductor systems. However, when the dimension of the system reduces to the nanometer scale, many problems emerge in the continuum k.p model. These include: (1) k vectors outside the valid k.p region, (2) no atomistic structure at the interfaces, which leads to wrong symmetry, spectrum splitting, and intervalley coupling, (3) controversial boundary conditions and spurious states, (4) no atomistic wavefunctions. To overcome these problems, we have developed an approach based on atomistic empirical pseudopotential method (EPM). The potentials are fitted to bulk band structures and the wavefunctions are expanded in plane waves basis. Using the folded spectrum method [1] and parallel computer, we are able to calculate the electronic structures of a million atom system. However, this requires tens of CPU hours on hundreds of processors. We have then developed a method, which expands the wavefunctions using the bulk band states. This strained linear combination of bulk band (SLCBB)[2] method enables one to calculate the electronic structures of a million atom system on one workstation within 10 hours, similar to the k.p computational effort. However, the SLCBB results are close to the direct calculation results (within 10-20 meV). They are based on the EPM Hamiltonian with atomistic details, thus avoid the k.p problems mentioned above. This method has been used to study embedded quantum dot spectra and multiexciton energy levels. [1] L.W. Wang, A. Zunger, J. Chem. Phys. 100, 2394(1994) [2] L.W. Wang, A. Zunger, Phys. Rev. B 59, 15806 (1999)