title: Colored spectrum characteristics of thermal noise on the molecular scale.
abstract: Thermal noise is of fundamental importance to many processes. Traditionally, thermal noise has been treated as white noise on the macroscopic scale. Using molecular dynamics simulations and power spectrum analysis, we show that the thermal noise of solute molecules in water is non-white on the molecular scale, which is in contrast to the conventional theory. In the frequency domain from 2 × 1011Hz to 1013Hz, the power spectrum of thermal noise for polar solute molecules resembles the spectrum of 1/f noise. The power spectrum of thermal noise for non-polar solute molecules deviates only slightly from the spectrum of white noise. The key to this phenomenon is the existence of hydrogen bonds between polar solute molecules and solvent water molecules. Furthermore, for polar solute molecules, the degree of power spectrum deviation from that of white noise is associated with the average lifetime of the hydrogen bonds between the solute and the solvent molecules.
authors: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China. wanrongzheng@sinap.ac.cn and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Zhi
authors: Z
authors: Zhu
authors: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China. wanrongzheng@sinap.ac.cn.
authors: Nan
authors: N
authors: Sheng
authors: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China. wanrongzheng@sinap.ac.cn.
authors: Haiping
authors: H
authors: Fang
authors: Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, China. wanrongzheng@sinap.ac.cn.
authors: Rongzheng
authors: R
authors: Wan