We have performed transport and ' C NMR measurements on the sulfur-based Bechgaard salt, (TMTTF) 2Br, at different pressures.At low pressures the ground state antiferromagnetism is commensurate with the lattice, while at high pressures many signatures of incommensurate density waves are found. Evidence that the transition, or crossover, between the two regimes is coincident with the suppression of a charge gap induced by coupling of the electronic states to the anion potential is presented.PACS numbers: 75.30.Fv, 72. 15.Nj, 76.60.Cq The Bechgaard salts are a series of compounds with the empirical formula (TMTCF)2X (C = Se, S, X = Re04, PF6, FSO3, etc. ) in which an extraordinarily wide variety of cooperative phenomena are manifested, including superconductivity, spin-density waves, order-disorder transitions, magnetic-field-induced transitions, and charge

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Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.