ERCS24: An updated version of the ERCS08 program for calculations of the cross sections for atomic electron removal based on the ECPSSR theory and its variants

ERCS24, an updated version of the ERCS08 program, calculates the atomic electron removal cross sections. It is written in FORTRAN in order to make it more portable and easier to customize by a large community of physicists, but it also comes with a separate windows graphics user interface control application ERCS24w that makes it easy to quickly prepare the input file, run the program, as well as view and analyze the output. The calculations are based on the ECPSSR theory for direct (Coulomb) ionization and non -radiative electron capture. With versatility in mind, the program allows for selective inclusion or exclusion of individual contributions to the cross sections from effects such as projectile energy loss, Coulomb deflection of the projectile, perturbation of electron's stationary state (polarization and binding), as well as relativity. This makes it straightforward to assess the importance of each effect in a given collision regime. The control application also makes it easy to setup for calculations in inverse kinematics (i.e. ionization of projectile ions by target atoms or ions). New version program summary: Program title: ERCS24 CPC Library link to program files: https://doi.org/10.17632/5yny6nc9x9.1 Licensing provisions: MIT Programming language: FORTRAN (using double precision) Journal reference of previous version: Comput. Phys. Commun. 180 (2009) 995-1003. Does the new version supersede the previous version?: Yes Reasons for the new version and brief descriptions of the revisions: (1) Since GNU FORTRAN compiler is widely available at no charge, it is adopted as a standard. Even though the source code of the original version of this program (ERCS08) can be successfully compiled by GNU FRORTRAN compiler and linked without any errors or warnings, problems related to standard input and output do occur at run time. These problems are corrected in the current version of the program (ERCS24), as tested by the latest available versions of the compiler (gFortran 13.2.0-32 and 13.2.0-64) [1]. Specifically, the stop' 'statement (line 279 in the original source code) has been commented out, while reading from the input file ERCS.dat and writing to the output file ERCS.out, originally assigned to input/output (I/O) units 5 and 6 are now assigned to I/O units 3 and 4, respectively. (2) Erroneous expressions for ECPSSR cross sections for K- and L-shell ionization by relativistic proton projectiles [2] were replaced by the correct ones [3]. Accuracy of the results was verified by reproducing the data from Fig. 4 of Ref. [2]. (3) Erroneous expressions for limits of integration of the electron transition form factor [4] were corrected as suggested by Symit and Lapicki [5]. Accuracy of the results was verified by reproducing the data from Table 2 of Ref. [5]. This correction primarily affects calculations for collisions in the adiabatic regime. In the notation of Refs. [5,6], the correct limits of integration of the electron transition form factor over scaled square of the momentum transfer (Q) and energy transfer (W) are Qa = mu(2)(R)y(R)Theta(2) [1-root 1 - 1/(mu(R)Theta(R)(y)n(2)(2))](2), Q(b) = mu(2)(R)y(R)Theta(2) [1 +root 1 - 1/(mu(R)Theta(R)(y)n(2)(2)), W-a = Theta/n(2)(2), and W-Q = 2 root Qy(R)Theta(2) - Q/mu(R), where Theta=zeta(s)theta(s), y(R)=m(s)(R)y=m(s)(R)eta(s)/Theta(2)=eta(R)(s)/Theta(2), and mu(R)=mu/m(s)(R). (4) Values of the fundamental physical quantities used in the calculations were updated and are now taken from the most recent recommended set currently available [7]. (5) The list of chemical element names in file ElementList.txt has been updated. (6) The windows graphics user interface ERCS08w was updated to ERCS24w. It was compiled as a 64 -bit application using the latest freely available version of the Microsoft (TM) Visual Studio (VS 2020) [8]. (7) Program license terms have been updated. Nature of problem: ECPSSR has become a typical tag word for a theory that goes beyond the standard plane wave Born approximation (PWBA) in order to predict the cross sections for direct (Coulomb) ionization of atomic electrons by projectile ions, taking into account the energy loss (E) and Coulomb deflection (C) of the projectile, as well as the perturbed stationary state (PSS) and relativistic nature (R) of the target electron. Its treatment of non -radiative electron capture to the projectile goes beyond the Oppenheimer-Brinkman-Kramers approximation (OBK) to include the effects of C, PSS, and R. PSS is described in terms of increased target electron binding (B) due to the presence of the projectile in the vicinity of the target nucleus, and (for direct ionization only) polarization of the target electron cloud (P) while projectile is outside the electron's shell radius. Several modifications of the theory have been recently suggested or endorsed by one of its authors (Lapicki). These modifications are sometimes explicit in the tag word (for example, eCPSSR, eCUSR, ReCPSShsR, etc.) A cross section for the ionization of a target electron is assumed to equal the sum of the cross sections for direct ionization (DI) and electron capture (EC). Additional comments: (i) Restrictions: The program is restricted to the ionization of K, L, and M electrons. The theory is non-relativistic, which effectively limits its applicability to projectile energies up to about 50 MeV/amu. However, the theory is extended to apply to relativistic light projectiles. Radiative electron capture is not taken into account, since its contribution is found to be negligible in the collision regimes covered by the ECPSSR theory. (ii) Unusual features: Windows graphics user interface along with a FORTRAN code for calculations, selective inclusion or exclusion of specific corrections, inclusion of the extension to relativistic light projectiles, inclusion of non-radiative electron capture.