The Multi-Phase Particle-In-Cell (MP-PIC) method is a numerical simulation technique employed for modeling multi phase flows, particularly those involving particles suspended within a fluid medium, such as particles used as the information carriers in Molecular Communication (MC). Building upon the existing MP-PIC solver (MPPICFoam) from the Open Field Operation and Manipulation (OpenFOAM) software suite, which does not support diffusion, this paper introduces a novel Diffusive MPPICFoam (DMPPICFoam) solver that integrates the random walk behavior (diffusion) of particles, thereby enhancing the realism of the simulation. Our proposed solver, the DMPPIC-Foam, is designed to more accurately model complex scenarios within the transition and dispersive regimes, such as those encountered in human capillaries. A comparative analysis between the proposed DMPPICFoam solver and the original MPPICFoam solver demonstrates significant improvements in the simulation of Channel Impulse Responses (CIRs) in two MC scenarios.