Journal Article Hartree potential Poisson solver Research Support, Non-U.S. Gov't charge density conjugate gradients fast multipole method femtosecond laser pulses h-BN films interpolating scaling functions linear scaling magnetoelastic effect multiferroic materials multigrid nano-domains parallel fast Fourier transform parallelization second harmonic generation skyrmions spintronics thermal conductivity time-dependent density functional theory topological materials twist-interfaces