含和不含Zn2 +的乙酰组氨酸原异构体的相对能量学和能量方法的基准
Relative energetics of acetyl-histidine protomers with and without Zn2+ and a benchmark of energy methods
摘要：
我们研究了乙酰组氨酸（AcH），裸露或微溶剂化与锌阳离子模拟隔离。首先，结合经验和第一性原理方法，对势能面的最小值进行全局搜索，分别针对五种可能的质子化状态中的任何一种。带负电荷的乙酰胆碱的互变异构形式之间的比较最稳定的结构显示出一个明确的偏好与中性咪唑环质子化的N-咪唑-2原子的构象。当向体系中加入锌阳离子时，情况相反，N-δ-1-质子化结构在能量上更有利。获得的最小结构，然后作为基准研究的基础，以检查常用的理论水平，即力场，半经验方法，密度泛函近似（DFA），和基于波函数的方法相对于高层次的耦合集群计算，即DLPNO-CCSD（T）方法的优点。所有测试的力场和半经验的方法表现出很差的性能在再现的构象，特别是涉及锌阳离子的系统的能量层次。Meta-GGA、混合、双混合DFA和MP2方法能够在化学准确度内描述参比方法的能量学，即平均绝对误差小于1 kcal/mol。最好的性能被发现为双杂交DFA B3 LYP + XYG 3的平均绝对误差为0.7千卡/摩尔和1.8千卡/摩尔的最大误差。虽然MP2与B3 LYP + XYG 3的性能相似，但由于精确结果所需的大基组，计算成本（即计时）相比增加了4倍。
英文摘要：
We studied acetylhistidine (AcH), bare or microsolvated with a zinc cation by simulations in isolation. First, a global search for minima of the potential energy surface combining both, empirical and first-principles methods, is performed individually for either one of five possible protonation states. Comparing the most stable structures between tautomeric forms of negatively charged AcH shows a clear preference for conformers with the neutral imidazole ring protonated at the N-epsilon-2 atom. When adding a zinc cation to the system, the situation is reversed and N-delta-1-protonated structures are energetically more favorable. Obtained minima structures then served as basis for a benchmark study to examine the goodness of commonly applied levels of theory, i.e. force fields, semi-empirical methods, density-functional approximations (DFA), and wavefunction-based methods with respect to high-level coupled-cluster calculations, i.e. the DLPNO-CCSD(T) method. All tested force fields and semi-empirical methods show a poor performance in reproducing the energy hierarchies of conformers, in particular of systems involving the zinc cation. Meta-GGA, hybrid, double hybrid DFAs, and the MP2 method are able to describe the energetics of the reference method within chemical accuracy, i.e. with a mean absolute error of less than 1kcal/mol. Best performance is found for the double hybrid DFA B3LYP+XYG3 with a mean absolute error of 0.7 kcal/mol and a maximum error of 1.8 kcal/mol. While MP2 performs similarly as B3LYP+XYG3, computational costs, i.e. timings, are increased by a factor of 4 in comparison due to the large basis sets required for accurate results.
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