中文摘要：

在密度函数理论的基础上,采用中性原子叠加模型和有限差分方法（SNA-FD）计算了石墨,金刚石和C60这三种碳的同素异形体中的正电子分布和湮没情况.计算表明,在片层结构的石墨晶体中,正电子主要在石墨层间的空隙中湮没,计算出的石墨中的正电子寿命为208ps,与文献中的实验结果210ps符合很好.在金刚石单晶中,正电子主要在碳原子之间的空隙中存在并发生湮没,计算出的金刚石中的正电子寿命为115.9ps,与文献中的实验结果110ps相符合;在面心立方结构的C60晶体中,正电子主要在C60分子球壳内外侧及分子之间存在,C60球形分子中心正电子分布很少,正电子的湮没区域集中在C60分子之间的空隙区域,计算出的C60中的正电子寿命为352ps,与文献中的实验结果350ps—400ps相符合.

英文摘要：

Superposed-neutral-atom model and the finite-difference method （SNA-FD） are used to calculate the positron annihilation lifetime in graphite, diamond and C60. We find that in graphite with laminar structure, the main place where the positron exists and annihilation takes place is the space between graphite layers. Positron lifetime of graphite is calculated to be 208 ps, which agrees with the published experimental result. In diamond, the main place where positron exists and annihilation takes places is the space between carbon atoms. Positron lifetime of diamond is calculated to be 115.0 ps, which agrees with the published experimental result. In C60 with a fcc structure, the main area where positron exits is the space near the spherical molecule shell of C60 and the space between molecules. The main area where positron annihilation takes place is the space between molecules. Positron lifetime of C60 is calculated to be 352 ps, which falls in the range of positron lifetime of C60 published in literature.