ELSEPA - Dirac partial-wave calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules
ELSEPA - Dirac partial-wave calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules
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DOI：
10.1016/j.cpc.2004.09.006
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发表时间：
2005-01-15
影响因子：
6.3
通讯作者：
Powell, CJ
中科院分区：
文献类型：
--
作者：
Salvat, F;Jablonski, A;Powell, CJ
介绍了用于计算电子和正电子被原子、正离子和分子弹性散射的FORTRAN 77代码系统ELSEPA。这些代码针对由局域中心相互作用势V(r)引起的散射进行相对论（狄拉克）分波计算。对于原子和离子，采用静态场近似，势等于入射粒子与靶之间的静电相互作用能，当入射粒子为电子时，还加上近似的局域交换相互作用。对于动能高达10 keV的入射粒子，势可选择性地包含一个半经验的关联 - 极化势，以描述靶电荷极化率的影响。此外，对于能量小于1 MeV的入射粒子，可引入一个虚吸收势，以解释由开放的非弹性通道导致的入射粒子波函数的衰减。分子截面通过单散射独立原子近似来计算，其中束缚原子的电子密度由自由中性原子的电子密度近似。固体中单个原子的弹性散射通过 muffin - tin模型势来描述。在普通个人计算机上，对于能量高达约5 MeV的情况，分波计算是可行的。ELSEPA代码还实现了近似分解方法，允许快速计算高得多的能量下的弹性截面。计算中采用的相互作用模型由用户通过组合代码提供的不同选项来定义。核电荷分布可在四种分析模型（点核、均匀带电球体、费米分布和赫尔姆均匀 - 均匀分布）中选择。原子电子密度以数值形式处理。该分发软件包包括从多组态狄拉克 - 福克自洽计算得到的从氢到铹（Z = 1 - 103）元素的中性原子电子密度的数据文件。为了比较，还包括对中性原子电子密度的三种简单分析近似（对应于托马斯 - 费米、托马斯 - 费米 - 狄拉克和狄拉克 - 哈特里 - 福克 - 斯莱特模型）。对于离子弹性散射的计算，电子密度应由用户提供。电子散射的交换势可在三种不同的分析近似（托马斯 - 费米、弗内斯 - 麦卡锡、赖利 - 特鲁哈拉）中选择。关联 - 极化势的可选方案基于经验的白金汉势。虚吸收势根据萨尔瓦特提出的局域密度近似计算[《物理评论A》68（2003）012708]。
The FORTRAN 77 code system ELSEPA for the calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules is presented. These codes perform relativistic (Dirac) partial-wave calculations for scattering by a local central interaction potential V (r). For atoms and ions, the static-field approximation is adopted, with the potential set equal to the electrostatic interaction energy between the projectile and the target, plus an approximate local exchange interaction when the projectile is an electron. For projectiles with kinetic energies up to 10 keV, the potential may optionally include a semiempirical correlation-polarization potential to describe the effect of the target charge polarizability. Also, for projectiles with energies less than 1 MeV, an imaginary absorptive potential can be introduced to account for the depletion of the projectile wave function caused by open inelastic channels. Molecular cross sections are calculated by means of a single-scattering independent-atom approximation in which the electron density of a bound atom is approximated by that of the free neutral atom. Elastic scattering by individual atoms in solids is described by means of a muffin-tin model potential. Partial-wave calculations are feasible on modest personal computers for energies up to about 5 MeV. The ELSEPA code also implements approximate factorization methods that allow the fast calculation of elastic cross sections for much higher energies. The interaction model adopted in the calculations is defined by the user by combining the different options offered by the code. The nuclear charge distribution can be selected among four analytical models (point nucleus, uniformly charged sphere, Fermi's distribution and Helm's uniform-uniform distribution). The atomic electron density is handled in numerical form. The distribution package includes data files with electronic densities of neutral atoms of the elements hydrogen to lawrencium (Z = 1-103) obtained from multiconfiguration Dirac-Fock self-consistent calculations. For comparison purposes, three simple analytical approximations to the electron density of neutral atoms (corresponding to the Thomas-Fermi, the Thomas-Fermi-Dirac and the Dirac-Hartree-Fock-Slater models) are also included. For calculations of elastic scattering by ions, the electron density should be provided by the user. The exchange potential for electron scattering can be selected among three different analytical approximations (Thomas-Fermi, Fumess-McCarthy, Riley-Truhlar). The offered options for the correlation-polarization potential are based on the empirical Buckingham potential. The imaginary absorption potential is calculated from the local-density approximation proposed by Salvat [Phys. Rev. A 68 (2003) 012708].