Influence of Force Fields and Quantum Chemistry Approach on Spectral Densities of BChl a in Solution and in FMO Proteins
Influence of Force Fields and Quantum Chemistry Approach on Spectral Densities of BChl a in Solution and in FMO Proteins
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DOI：
10.1021/acs.jpcb.5b03654
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发表时间：
2015-08-06
影响因子：
3.3
通讯作者：
Kleinekathoefer, Ulrich
中科院分区：
文献类型：
--
作者：
Chandrasekaran, Suryanarayanan;Aghtar, Mortaza;Kleinekathoefer, Ulrich
在Fenna马修斯Olson（FMO）复合物的激子动力学中发现长寿命量子相干现象后，捕光（LH）系统的研究引起了人们的广泛关注。在这种复合物中，激发能在细菌叶绿素a（BChla）色素之间传递。两个量子力学/分子力学（QM/MM）的研究，每一个不同的力场和quantinn化学的方法，报告了不同的激发能分布的FMO复合物。为了了解预测激发能存在这些差异的原因，我们对使用CHARMM和的模拟进行了比较研究。AMBER力场和Zerner中间忽略微分轨道（ZINDO）/S和含时密度泛函理论（TDDFT）量子化学方法。使用CHARMM力场与ZINDO/S或TDDFT的计算总是显示出比使用AMBER力场的能量分布更宽的范围。这些能量分布中的高能或低能尾部导致低频处的谱密度值较大。对溶液中单个BChla分子的详细研究表明，在没有环境的情况下，两种力场组的态密度是相同的。然而，包括环境点电荷，激发能分布变得更宽，并且取决于所应用的方法，也是不对称的。使用TDDFT与AMBER力场一起预测的激发能分布显示出对称的高斯分布。
Stnclies on light-harvesting (LH) systems have attracted much attention after the finding of long-lived quantum coherences in the exciton dynamics of the Fenna Matthews Olson (FMO) complex. In this complex, excitation energy transfer Occurs between the bacteriochlorophyll a (BChl a) pigments. Two quantum mechanics/molecular mechanics (QM/MM) studies, each with a different force-field and quantinn chemistry approach, reported different excitation energy distributions for the FMO complex. To understand the reasons for these differences in the predicted excitation energies, we have carried out a comparative study between the simulations using the CHARMM and. AMBER force field and the Zerner intermediate neglect of differential orbital (ZINDO)/S and time-dependent density functional theory (TDDFT) quantum chemistry methods. The calculations using the CHARMM force field together with ZINDO/S or TDDFT always show a wider spread in the energy distribution compared to those using the AMBER force field. High- or lowenergy tails in these energy distributions result in larger values for the spectral density at low frequencies. A detailed study on individual BChl a molecules in solution shows that without the environment, the derisity of states is-the same for both force field sets. Including the environmental point charges, however, the excitation energy distribution gets broader and, depending on the applied methods, also asymmetric. The excitation energy distribution predicted using TDDFT together with the AMBER force field shows, a symmetric, Gaussian-like distribution.