The radial drift and diffusion of dust particles in protoplanetary disks affect both the opacity and temperature of such disks as well as the location and timing of planetesimal formation .
In this paper , we present results of numerical simulations of particle-gas dynamics in protoplanetary disks that include dust grains with various size distributions .
We consider three scenarios in terms of particle size ranges , one where the Stokes number \tau _ { s } = 10 ^ { -1 } -10 ^ { 0 } , one where \tau _ { s } = 10 ^ { -4 } -10 ^ { -1 } and finally one where \tau _ { s } = 10 ^ { -3 } -10 ^ { 0 } .
Moreover , we consider both discrete and continuous distributions in particle size .
In accordance with previous works we find in our multi-species simulations that different particle sizes interact via the gas and as a result their dynamics changes compared to the single-species case .
The larger species trigger the streaming instability and create turbulence that drives the diffusion of the solid materials .
We measure the radial equilibrium velocity of the system and find that the radial drift velocity of the large particles is reduced in the multi-species simulations and that the small particle species move on average outwards .
We also vary the steepness of the size distribution , such that the exponent of the solid number density distribution , d \it { N } / d \it { a } \propto \it { a ^ { - q } } , is either q = 3 or q = 4 .
We overall find that the steepness of the size distribution and the discrete versus continuous approach have little impact on the results .
The level of diffusion and drift rates are mainly dictated by the range of particle sizes .
We measure the scale height of the particles and observe that small grains are stirred up well above the sedimented midplane layer where the large particles reside .
Our measured diffusion and drift parameters can be used in coagulation models for planet formation as well as to understand relative mixing of the components of primitive meteorites ( matrix , chondrules and CAIs ) prior to inclusion in their parent bodies .