Title: A Variational Approach to Trap Macromolecules

Abstract: Trapping macromolecules is impoartant for the study of their conformations, interactions, dynamics and kinetic processes. Here, we develop a variational approach which self-consistently introduces a mean force that controls the center-of-mass position and a self-adjustable harmonic potential that counters the center-of-mass fluctuation. The effectiveness and versatility of our approach is verified in three classical yet not fully understood problems in polymer physics: (1) single-chain conformation in the entire solvent regimes, (2) globule-pearl necklace-coil transition of a polyelectrolyte and (3) inter-chain interaction by simultaneously trapping two polymers. The scaling relationships and $\theta$ behaviors are well captured. Conformations with large shape anisotropy appearing in charged polymers are clearly depicted. Our theoretical predictions are in quantitative agreement with experimental results reported in the literature.