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We present an efficient polarizable electrostatic model, utilizing typed, atom-centered polarizabilities and the fast direct approximation, designed for efficient use in molecular dynamics (MD) simulations. The model provides two convenient approaches for assigning partial charges in the context of atomic polarizabilities. One is a generalization of RESP, called RESP-dPol, and the other, AM1-BCC-dPol, is an adaptation of the widely used AM1-BCC method. Both are designed to accurately replicate gas-phase quantum mechanical electrostatic potentials. Benchmarks of this polarizable electrostatic model against gas-phase dipole moments, molecular polarizabilities, bulk liquid densities, and static dielectric constants of organic liquids show good agreement with the reference values. Of note, the model yields markedly more accurate dielectric constants of organic liquids, relative to a matched nonpolarizable force field. MD simulations with this method, which is currently parametrized for molecules containing elements C, N, O, and H, run only about 3.6-fold slower than fixed charge force fields, while simulations with the self-consistent mutual polarization average 4.5-fold slower. Our results suggest that RESP-dPol and AM1-BCC-dPol afford improved accuracy relative to fixed charge force fields and are good starting points for developing general, affordable, and transferable polarizable force fields. The software implementing these approaches has been designed to utilize the force field fitting frameworks developed and maintained by the Open Force Field Initiative, setting the stage for further exploration of this approach to polarizable force field development.

The problem of steering pyramid control moment gyro (CMG) cluster for fast spacecraft attitude maneuver along eigenaxis is investigated. A novel steering law is proposed to continuously attempt to reduce the difference between the current gimbal angle and the desired one corresponding to the angular momentum envelop of the CMG cluster. The proposed steering law can be decomposed into two parts: the first one is a singularity robust term to keep maneuverability and produce control torque, and the other is a null motion term to rearrange the gimbal angles toward momentum envelope. By involving this steering law, it is expected to possess both rapid angular momentum exchange and singularity avoidance ability. In addition, by introducing a new limit vector on attitude error, classical cascade-saturation control algorithm is revised to guarantee spacecraft eigenaxis rotation. Both open-loop steering law test and closed-loop attitude maneuver simulations are performed to evaluate the efficacy of the proposed methods. [ABSTRACT FROM AUTHOR]