Understanding performance and limitation of CsTe photocathodes under high field gradients in a radio-frequency gun requires adequate theoretical models for material properties, photoemission and surface morphology. We are developing a suite of models based on Density Functional Theory (DFT), moment and Monte-Carlo (MC) photoemission models, and meso-scale material surface model informed by DFT and Molecular Dynamic (MD) simulations. Our DFT calculations provide detailed structural, elastic, electronic, optical, and transport properties of CsTe for photoemission applications. Temperature, density of states, and thin film optical effects have recently been incorporated in a moment-based photoemission model, while the high field effects for electron transport and emission are being modeled in the MC model. Our meso-scale surface model addresses surface morphology under high field stress and surface heating. Machine-learning technique has also been used to enhance the DFT and MD calculations for CsTe. This poster will present an overview of these theoretical models and their results with applications to the LANL CARIE project and other relevant experiments.