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Difficulties of Popular Density Functionals to Describe the Conformational Isomerism in Iodoacetic Acid.
The Journal of Physical Chemistry A ( IF 2.9 ) Pub Date : 2020-06-21 , DOI: 10.1021/acs.jpca.0c03322
J Philipp Wagner 1
Affiliation  

Matrix isolation studies in solid argon and neon at 4.2 K reveal that iodoacetic acid initially only exists as its ground state (c,x) conformer with an almost perpendicular I–C–C═O dihedral angle, but UV irradiation in the 240–255 nm range leads to population of the 0.8 kcal mol–1 less stable (c,c) isomer. The latter structure exhibits a close 3.23 Å contact of the iodine and carbonyl oxygen atoms decidedly below the sum of their van der Waals radii (3.50 Å). Increasing the matrix temperature by only a few Kelvin triggers the thermal back reaction of (c,c) to (c,x) and leads to an estimated upper limit of 0.38 kcal mol–1 for the associated torsional barrier. While wave function methods including completely uncorrelated Hartree–Fock theory have no problem to identify (c,c) as a proper minimum, many popular density functionals fail to describe the C–C torsional potential in cis-iodoacetic acid qualitatively correct. We assessed the performance of 12 density functionals of different levels of sophistication, namely, the BLYP, PBE, TPSS, B3LYP, BHandHLYP, PBE0, M06-2X, CAM-B3LYP, ωB97X-D3, B2-PLYP, B2GP-PLYP, and DSD-PBEP86 methods, against accurate extrapolated CCSD(T)/CBS(T–Q)//MP2/def2-TZVPP energies and found that almost all of them yield acceptable relative energies. Still, even some of the best performers fail to find a reasonably deep minimum in the region of the (c,c) conformer, and addition of the empirical D3-dispersion correction does not remedy the qualitative shortcoming. Instead, inclusion of a sufficient amount of (long-range) exact exchange and likely a proper treatment of medium-range correlation effects all along the torsional coordinate play an important role in the proper description of the sub-van der Waals iodine–oxygen contact. More modern, recommended functionals do not suffer from the described shortcoming.

中文翻译:

流行的密度泛函难以描述碘乙酸中的构象异构现象。

在4.2 K的固体氩气和氖气中进行的基质分离研究表明,碘乙酸最初仅以其基态(cx)构象存在,几乎具有垂直的I–C–C═O二面角,但在240–255范围内受到紫外线照射纳米范围会导致0.8 kcal mol –1的不稳定异构体(cc)的填充。后一种结构显示出碘和羰基氧原子的紧密3.23Å接触,确定低于它们的范德华半径之和(3.50Å)。仅将基体温度提高几个开尔文,就会触发(cc)到(cx)的热逆反应),导致相关的扭转屏障的估计上限为0.38 kcal mol –1。尽管波函数方法,包括完全不相关哈特里-福克理论也没有问题,以确定(çÇ)作为一个适当的最小值,许多流行的密度泛函没有描述在C-C扭转潜在-碘乙酸定性正确。我们评估了12种不同复杂程度的密度泛函的性能,即BLYP,PBE,TPSS,B3LYP,BHandHLYP,PBE0,M06-2X,CAM-B3LYP,ωB97X-D3,B2-PLYP,B2GP-PLYP和DSD-PBEP86方法针对准确外推的CCSD(T)/ CBS(T–Q)// MP2 / def2-TZVPP能量,发现几乎所有方法都能产生可接受的相对能量。尽管如此,即使是一些表现最好的企业也未能在(cc)一致性,并添加经验性D3色散校正不能弥补定性缺点。取而代之的是,包括足够量的(远距离)精确交换以及可能在整个扭转坐标系中适当处理中等距离相关效应在正确描述范德华力碘-氧接触中起着重要作用。 。更现代的推荐功能不会遭受上述缺点的困扰。
更新日期:2020-07-09
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