Qiang, J. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-WEA3IO02 English 838-842 WEA3IO02 ion linac controls electron FEL Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-WEA3IO02 https://jacow.org/napac2016/papers/wea3io02.pdf State-of-the-art tools have been developed that allow start-to-end modeling of the beam formation at the cathode, to its transport, acceleration, and delivery to the undulator. Algorithms are based on first principles, enabling the capture of detailed physics such as shot-noise driven micro-bunching instabilities. The most recent generation of the IMPACT code, using multi-level parallelization on massively parallel supercomputers, now enables multi-objective parametric optimization. This is facilitated by recent advances such as the unified differential evolution algorithm*. The most recent developments will be described, together with applications to the modeling of LCLS-II**.