Comment on “The Nature of Chalcogen‐Bonding‐Type Tellurium–Nitrogen Interactions”: Fixing the Description of Finite‐Temperature Effects Restores the Agreement Between Experiment and Theory

Abstract

Mitzel and co-workers recently presented an intriguing molecule displaying a tellurium-nitrogen interaction. Structural data obtained in the solid and in gas phase indicated a large increase of the Te-N equilibrium distance r e from 2.64 to 2.92 , respectively. Although some DFT calculations appear to support the large r e in gas phase, we argue that the lions share of the increase is due to an incomplete description of finite-temperature effects in the back-corrected experimental data. This hypothesis is based on high-level coupled-cluster (CC) and periodic DFT calculations, which consistently point towards a much smaller r e in the isolated molecule. Further support comes through MD simulations with a tuned GFN2-xTB Hamiltonian: Calibrated against a CC reference, these show a six-times larger influence of temperature than with the originally used GFN1-xTB. Taking this into account, the backcorrected r e in gas phase becomes 2.67 AE 0.08 , in good agreement with high-level CC theory and most DFT methods.Non-covalent interactions (NCIs) are fundamental to the three dimensional structure of matter. [1][2][3][4][5][6] By developing a better understanding for them, [7][8][9][10][11][12] chemists have gained access to many new ways to shape matter, e.g., through selfassembly of large molecules in solution or pattern recognition. [6,[13][14][15][16][17][18][19] Emerging from this line of research, several novel NCI motifs have been suggested and debated in recent

Best‐Practice DFT Protocols for Basic Molecular Computational Chemistry**

“…We note that the applicability of low-level semi-empirical methods should be carefully checked if exotic bonds, transition metals, or heavy main-group elements are present. [131] The only complication that arises concerning the use of lower-level methods for frequencies is that the structure for which the vibrational frequencies are calculated has to be an energy minimum at this very level (fully optimized, vanishing atomic forces). Otherwise, the presence of many artificial imaginary frequencies severely limits the accuracy of the calculated thermostatistical corrections.…”

“…In many cases, it is even sufficient to obtain thermostatistical corrections at a semi‐empirical quantum mechanics level, e.g., with GFN2‐xTB, [5, 179] as shown in example 4.2. We note that the applicability of low‐level semi‐empirical methods should be carefully checked if exotic bonds, transition metals, or heavy main‐group elements are present [131] …”

Best Practice DFT Protocols for Basic Molecular Computational Chemistry

“…Therefore, a systematic deviation compared to experimental data at finite temperatures is expected as standard equilibrium structure treatments, such as geometry optimizations, do not include nuclear zero-point vibrations (ZPV), vibrational (thermally) bonds-elongation, or entropy effects. In other words, a perfect agreement between experimental structures obtained at finite temperature and those calculated at T=0 K is not necessarily desirable since -sometimes substantial [131][132][133] -finite-temperature effects can cause a significant bias. However, for common covalent bonds between typical atoms, these effects are too small to have a significant influence.…”

“…We note that applicability of low-level semi-empirical methods should be carefully checked if exotic bonds, transition metals, or heavy main-group elements are present. 131 The only complication that arises concerning the use of lowerlevel methods for frequencies is that the structure for which the vibrational frequencies are calculated has to be an energy minimum at this very level (fully optimized, vanishing atomic forces). Otherwise, the presence of many artificial imaginary frequencies severely limits the accuracy of the calculated thermostatistical corrections.…”

Best Practice DFT Protocols for Basic Molecular Computational Chemistry

“…Therefore, a systematic deviation compared to experimental data at finite temperatures is expected as standard equilibrium structure treatments, such as geometry optimizations, do not include effects such as nuclear zero-point vibrational energy (ZPVE), vibrationally (thermally) elongated bonds, or molecular entropy. Accordingly, a perfect agreement between experimental structures obtained at finite temperature and those calculated at T=0 K is not necessarily desirable since -sometimes substantial [109][110][111] -finite-temperature effects can cause a significant bias. However, for common covalent bonds between typical atoms, these effects are too small to have a significant influence.…”