AMTsolver - Angular Momentum Transfer Solver

Overview

AMTsolver is a C++ program that calculates the spectral angular momentum (dL/dω) transferred to a nanoparticle (NP) due to interaction with a fast-moving electron. The calculation is performed by analytically solving the closed surface integral, resulting in a double multipolar sum expression. The program focuses exclusively on the external field contribution and calculates the total angular momentum transfer (ΔL) for different values of the impact parameter b.

Features

• Computes frequency integrals using Gauss-Kronrod quadrature with adaptive partition
• Saves spectral results to dldw_*.dat files
• Saves integrated angular momentum results to DL_*.dat files
• Supports multiple parameter sets via CLI
• Automatic convergence checking with configurable threshold
• Parallel computation support (via OpenMP)

Prerequisites

• C++17 compatible compiler (g++ recommended)
• Boost libraries (version 1.70+)
• complex_bessel library
• CLI11 (for command line parsing)

Installation

git clone https://github.com/yourusername/AMTsolver.git
cd AMTsolver
mkdir build

Standard build

g++ -Iinclude -c src/IN51.cpp -o build/IN51.o
g++ -Iinclude -Iinclude/Dielectric/DrudeAl -c src/main.cpp -o build/main.o -lcomplex_bessel
g++ build/IN51.o build/main.o -o bin/AMTsolver -lcomplex_bessel

Parallel build (OpenMP)

g++ -fopenmp -O2 -std=c++17 -Iinclude -c src/main.cpp -o build/main.o -lcomplex_bessel
g++ build/IN51.o build/main.o -o bin/AMTsolver -lcomplex_bessel -fopenmp```

Basic Command (example)

./AMTsolver -a <radius_nm> -b <impact_param_nm> -v <velocity>

Single Calculation

./AMTsolver -a 50.0 -b 55.0 -v 0.7

Velocity Scan (20 points)

./AMTsolver -a 50.0 -b 55.0 --vscan -n 20

Impact parameter scan

./AMTsolver -a 50.0 -v 0.7 --bscan -n 30 -e 1e-5

Command Line Options

Option	Description	Default Value	Constraints
-a <float>	Nanoparticle radius (nm)	1.0	Must be > 0
-b <float>	Impact parameter (nm)	1.5	Must be > NP radius (-a)
-v <float>	Electron velocity (fraction of c)	0.7	0.0 ≤ v ≤ 0.999
--vscan	Enable velocity scan mode	false	Requires -n for point count
--bscan	Enable impact parameter scan mode	false	Requires -n for point count
--contour	Enable velocity vs. impact parameter contour	false	Combines --vscan and --bscan
-e <float>	Convergence threshold	1e-4	Must be > 0
-n <int>	Number of points in scans	9	Must be ≥ 2
-m <int>	Minimum multipole order (ℓ)	1	Must be ≥ 1

Notes:

• All numerical values must be positive
• Scans generate data files in the output directory structure
• Contour mode generates 2D parameter space analysis

Output structure

results/
└── material=<material>/
    └── a=<radius>nm/
        └── <timestamp>/
            ├── v_scan_for_b=<impact_param>nm/  # Velocity scans
            │   ├── Lmax=<value>/
            │   │   ├── DLy_<params>.dat
            │   │   └── error_DLy_<params>.dat
            │   └── MultipolarConvergence/
            │       └── MultipolarConvergence_<params>.dat
            ├── b_scan_for_v=<velocity>c/       # Impact param scans
            │   └── ... 
            └── simulation_parameters.txt       # Metadata

For citations

@software{AMTsolver, author = {Jorge Luis Briseño-Gómez}, title = {AMTsolver: Angular Momentum Transfer Calculator}, year = {2023}, publisher = {GitHub}, journal = {GitHub repository}, howpublished = {\url{https://github.com/LuisBrise/AMTsolver}}