Schappals Michael, Mecklenfeld Andreas, Kröger Leif, Botan Vitalie, Köster Andreas, Stephan Simon, García Edder J, Rutkai Gabor, Raabe Gabriele, Klein Peter, Leonhard Kai, Glass Colin W, Lenhard Johannes, Vrabec Jadran, Hasse Hans
Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern , Kaiserslautern, Germany.
Institut für Thermodynamik (ift), Technische Universität Braunschweig , Braunschweig, Germany.
J Chem Theory Comput. 2017 Sep 12;13(9):4270-4280. doi: 10.1021/acs.jctc.7b00489. Epub 2017 Aug 7.
Thermodynamic properties are often modeled by classical force fields which describe the interactions on the atomistic scale. Molecular simulations are used for retrieving thermodynamic data from such models, and many simulation techniques and computer codes are available for that purpose. In the present round robin study, the following fundamental question is addressed: Will different user groups working with different simulation codes obtain coinciding results within the statistical uncertainty of their data? A set of 24 simple simulation tasks is defined and solved by five user groups working with eight molecular simulation codes: DL_POLY, GROMACS, IMC, LAMMPS, ms2, NAMD, Tinker, and TOWHEE. Each task consists of the definition of (1) a pure fluid that is described by a force field and (2) the conditions under which that property is to be determined. The fluids are four simple alkanes: ethane, propane, n-butane, and iso-butane. All force fields consider internal degrees of freedom: OPLS, TraPPE, and a modified OPLS version with bond stretching vibrations. Density and potential energy are determined as a function of temperature and pressure on a grid which is specified such that all states are liquid. The user groups worked independently and reported their results to a central instance. The full set of results was disclosed to all user groups only at the end of the study. During the study, the central instance gave only qualitative feedback. The results reveal the challenges of carrying out molecular simulations. Several iterations were needed to eliminate gross errors. For most simulation tasks, the remaining deviations between the results of the different groups are acceptable from a practical standpoint, but they are often outside of the statistical errors of the individual simulation data. However, there are also cases where the deviations are unacceptable. This study highlights similarities between computer experiments and laboratory experiments, which are both subject not only to statistical error but also to systematic error.
热力学性质通常由描述原子尺度相互作用的经典力场来建模。分子模拟用于从此类模型中获取热力学数据，为此有许多模拟技术和计算机代码可供使用。在本次循环研究中，探讨了以下基本问题：使用不同模拟代码的不同用户组在其数据的统计不确定性范围内能否获得一致的结果？定义了一组24个简单的模拟任务，并由使用八个分子模拟代码的五个用户组来解决：DL_POLY、GROMACS、IMC、LAMMPS、ms2、NAMD、Tinker和TOWHEE。每个任务包括：（1）由一个力场描述的纯流体的定义，以及（2）确定该性质的条件。这些流体是四种简单的烷烃：乙烷、丙烷、正丁烷和异丁烷。所有力场都考虑内部自由度：OPLS、TraPPE以及带有键伸缩振动的改进版OPLS。在一个指定的网格上确定密度和势能作为温度和压力的函数，使得所有状态均为液态。用户组独立工作并将结果报告给一个中央机构。只有在研究结束时才向所有用户组披露完整的结果集。在研究过程中，中央机构只提供定性反馈。结果揭示了进行分子模拟的挑战。需要进行几次迭代来消除重大误差。从实际角度来看，对于大多数模拟任务，不同组结果之间的剩余偏差是可以接受的，但它们往往超出了单个模拟数据的统计误差范围。然而，也存在偏差不可接受的情况。这项研究突出了计算机实验和实验室实验之间的相似性，二者不仅都受到统计误差的影响，还受到系统误差的影响。
