Structure formation of a quenched single polyethylene chain with different force fields in united atom molecular dynamics simulations

Katsumi Hagita,Susumu Fujiwara,Nobuyuki Iwaoka

doi:10.1063/1.5063438

Abstract

The differences in the structure formations of a single polyethylene (PE) chain in united atom molecular dynamics (UAMD) simulations under quenching was investigated with varying force fields (FFs) that included torsional potential. We estimated the crystallinity of the folded structures undergoing local crystallization of the single PE chain. In simulations with DREIDING FF, highly folded structures were observed with fast quenching at the rate of 50 K/ns. From the viewpoint of crystallinity, we clarified that it was easy to achieve folding of the PE chains into local crystals with DREIDING FFs. With recent commonly used general FFs such as OPLS-UA and TraPPE-UA, highly folded structures were observed by quenching at the rate of 1 K/5 ns. In the present paper, we examine the Rigby–Roe (RR) FF optimized by Theodorou and coworkers and Paul–Yoon–Smith (PYS) FF optimized by Rutledge and coworkers. With the RR-Theodorou and PYS-Rutledge FFs, crystallization was observed with quenching at 1 K/ns and 1 K/5 ns, respectively. Consequently, it was relatively easier to achieve folding with the RR-Theodorou FF than with the PYS-Rutledge, OPLS-UA, and TraPPE-UA FFs.

Highlights

Large-scale molecular dynamics (MD) simulation studies on the crystallization of polyethylene (PE) melts have been recently reported.[1,2,3,4,5,6,7] Various force fields (FFs) are employed in the MD simulations, and it is known that the crystal growth rate of PE is greatly influenced by their FF parameters
We performed the united atom molecular dynamics (UAMD) simulations with the DREIDING-united atom (UA) FF17 with and without modification, Rigby–Roe FF,[28] Paul–Yoon–Smith FF,[29] PYS FF optimized by Rutledge and coworkers,[30,31] Rigby–Roe FF optimized by Theodorou and coworkers,[37,38] OPLS-UA,[41] and TraPPE-UA.[42]
DREIDING-UA FF, the Paul–Yoon–Smith FF optimized by Rutledge and coworkers, the Rigby– Roe FF, the Rigby–Roe FF optimized by Theodorou and coworkers, OPLS-UA, and TraPPE-UA

Summary

Introduction

Large-scale molecular dynamics (MD) simulation studies on the crystallization of polyethylene (PE) melts have been recently reported.[1,2,3,4,5,6,7] Various force fields (FFs) are employed in the MD simulations, and it is known that the crystal growth rate of PE is greatly influenced by their FF parameters. Regarding the crystallization of PE, the spontaneous structure formation of a single long PE chain during the cooling process was investigated.[9,10,11,12] These studies motivated the establishment of simple models on protein folding[13,14] because the aim of experimental studies on folding of the single PE chain was to study protein folding.[15,16]

Methods

Results

Conclusion