Written by Humberto Jr (humberto.dasilvajr@unlv.edu).

Based on the original routine vlambda.f90 from Fabio Carelli (2015-2016).

Oct, 2019

This program computes the vibrational multipolar coefficients as function of the scattering coordinate, R, for an atom-diatom problem, defined as

where,

1. The phi functions are rovibrational wavefunctions with quantum number upsilon, from the diatomic target, as function of the internuclear distance r.

2. The V function is a potential energy surface of the system in Jacobi coordinates (r, R, theta).

3. And P represents Lengendre polynomials of order lambda evaluated at cos(theta).

1. Vibrational wavefunctions are expected in independent data files named v=0.dat, v=1.dat, v=2.dat etc, each of which with two columns of data: r and the probability amplitude. All blank lines or lines starting with # are ignored by the code.

2. The potential energy surface (PES) in Jacobi coordinates (r, R, theta) is defined by the user in pes.f90. On entry, units for (r, R) are the same of those used in the wavefunctions. Theta is in rad. On exit, the energy unit chosen is also the unit for all results.

3. Invoke either scripts/build_gfortran.sh or scripts/build_ifort.sh to compile the program, e.g. ./build_gfortran.sh (for GNU gfortran).

4. Write an input file, e.g. example/He+H2+_example.d; where, use_omp switchs on/off the use of OpenMP; v_dir is the folder in which the wavefuctions are stored; and, is_homo tells the program to consider a (hetero) homonuclear diatomic target.

5. Invoke the program, e.g. ./main.out < my_input_file.d

6. Each multipolar coefficient, as function of R, will be printed in independent files named v=0-0_lambda=0.dat, v=0-1_lambda=0.dat, etc. In which units are driven by the wavefunctions and the PES (see above).

7. One is required to write his own post-processing script to read the output data files and rewrite in the format used by ASPIN, Molscat or any other scattering code.

See Fig. (6) of Ref. [1] for details.

[1] I. Iskandarov et al. Eur. Phys. J. D 71:141 (2017) doi: https://doi.org/10.1140/epjd/e2017-80043-8