Dear fellow MEEP users, Recently I've tried to obtain the total optical trapping force on a polystyrene bead in water. The idea is as followed: I make several 3D MEEP simulations where I displace the bead to different positions in the field. Each time I calculate the optical force by using the Maxwell stress tensor and integrating over a box surface just surrounding the bead and time average the force over a couple of periods. A check for numerical errors is to calculate the force over the same box, yet this time without the bead. This should give a force close to zero as long as the dielectric constant is the same in and outside the box. However my program does not for a box position outside the center (errors are like half of the calculated value with the bead). For wavelength=0.750 (meep units), bead diameter 1 and even resolutions up to 30 do not reduce the error. Much higher resolutions are not an option for me. The ' synchronize-magnetic' option didn't help, (unless I'm using it wrong). Then I found this article (http://dx.doi.org/10.1016/S0252-9602(10)60009-4) in which they state that with the normal Yee lattice, the relative error in their bead trapping situation (in 2D) is large as well, and a resolution of wavelength/200 would be required to reduce the error to 10% (see figure 5 in article). Can I really forget about using MEEP for this type of purpose, or are there means of improvement, or counterarguing positive experiences with this type of work in MEEP? Thanks in advance, Thijs
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