Table 5. Calculations of the Aiso Parameter of the Nitroxy N/O Sites of HMI in Water Using the Reference Snapshot Configurations I and II (See Text) Based on QM/MM DLPNO-CCSD Single-Point Calculations Using Different QM Regions (See Text) Regarding the Inclusion up to the nth Solvation Shell (* Calculated on 8 Cores and ** Calculated on 16 Cores, See Text)a.
| QM region | reference system | time (h) | Aiso(14N/17O) (MHz) | Δref(14N/17O) (MHz) | #H2O treated with DLPNO-CCSD theory |
|---|---|---|---|---|---|
| HMI + full solvation | reference system I | 1560 | 44.3/–51.8 | 128 | |
| reference system II | 1200 | 45.2/–50.0 | 128 | ||
| HMI no solvation shell | reference system I | 11* | 42.4/–53.2 | 1.9/1.4 | 0 |
| reference system II | 16* | 44.8/–50.8 | 0.4/0.8 | 0 | |
| HMI + first solvation shell | reference system I | 15** | 44.1/–52.3 | 0.0/0.5 | 2 |
| reference system II | 19* | 44.8/–50.6 | 0.4/0.6 | 1 | |
| HMI + second solvation shell | reference system I | 36** | 44.3/–51.7 | 0.0/0.0 | 12 |
| reference system II | 39** | 45.1/–50.2 | 0.1/0.2 | 16 |
a
Note that DLPNO-CCSD yields Aiso values of 30.1 and −55.8 MHz for the nitrogen and oxygen atoms, respectively, for the gas-phase equilibrium structure of HMI (optimized using revPBE0-D3/def2-TZVPP). Δref = |AHMI+full solvationiso – AHMI+reduced solvation| where either “no solvation shell” or “1st solvation shell” or “second solvation shell” as mentioned in the table refers to reduced solvation.