First-Principle Study of Molecular Springs under Shear Deformation

Recently synthesized tunable molecular springs are investigated theoretically using massively parallel density functional simulations with the generalized gradient approximation. The springs are salts of organosilver complexes that crystallize in structures with monoclinic symmetry. For springs with NO₃^- (N-spring) and ClO₄^- (Cl-spring) ions as negative balancers, we are able to refine their X-ray structures. Our calculations of total energies as functions of the nonorthogonal lattice angle β correctly reproduce the experimental equilibrium values of the angle for both the N- and Cl-springs. For the N-spring, our calculations reveal that the nitrate ions undergo concerted propeller rotations in the clockwise direction as the angle increases by 10° around the experimental value. For the Cl-spring, the rotations of chlorate ions are more enhanced in a limited range of the β angle, but they move in the counterclockwise direction. For the N-spring, the potential energy curve is symmetric and the shear modulus is about 0.01TPa. Calculations of the electronic density of states show that both springs are semiconductors.