22
2 Computational Methods in Rh-Catalyzed C–H Functionalization
while most large enough basis sets can yield the same result in DFT calculations
[55]. Additionally, when the number of base functions for using a basis set is the
same, the time consuming can be saved by using a basis set with less Gaussian-type
function under the same precision [56]. Therefore, segmented contraction basis sets,
such as Pople’s basis sets and def2 series of basis sets, are the better choice in DFT
calculations [55, 57, 58].
For the computational study of Rh-catalyzed C–H functionalization, regular polarization functions are necessary, which can improve the accuracy to a great extent [59].
However, the larger angular momentum functions are unnecessary. A triple-zeta basis
set is usually slightly better than a double-zeta one [60, 61]. Followed this idea, 631G(d) is the smallest acceptable basis set for the description of the atoms except
for Rh metal in geometry optimizations [45, 62, 63]. The basis set of 6-311G(d,p) is
another better choice for both accuracy and efficiency [50, 64]. When def2 series of
basis set is used, def2-SVP is acceptable, while, def2-TZVP is a better one [65]. In
an anionic molecule, defuse functions are necessary, therefore, 6-31 + G(d) is the
acceptable basis set [44, 66]. To obtain accurate energy information, the polarization functions and defuse functions should be both taken into account in the energy
calculations. The first choice of basis set for the description of the atoms except for
Rh metal is 6-311 + G(d,p) followed by 6-31 + G(d) and 6-311G(d,p) in energy
calculations [63, 67–69].
For the DFT calculation onto Rh metal atom, employing a pseudo potential basis
set is strongly recommended for the consideration of both accuracy and efficiency.
In this area, LANL2DZ [70] is the smallest basis set for Rh metal atom, which only
provides only acceptable accuracy for some geometry optimizations and energy
calculations [62, 64, 67, 69]. The larger ones, such as SDD [71], LANL2TZ [70],
LANL08 [72], and LANL08(f) [73], are also recommended for Rh metal atom
[63, 68].
2.1.2 Solvent Effect
The solvent effect is crucial to Rh-catalyzed C–H functionalization, which should
always be considered in energy calculations. The solvent effect in homogeneous
catalysis calculations is considered by the implicit solvent model. In the implicit
solvent model, the solvent environment is simply considered as a polarizable continuous medium. The advantage of the implicit solvent model is that it can represent the
average effect of solvents without the consideration of various possible molecular
arrangements of solvent layer. The weakness is that the strong interaction between
solvent and solute cannot be represented, such as hydrogen bond. Moreover, the
accuracy of solvation energy for ionic solute cases is significantly lower than that of
neutral solute cases.
Dielectric formulation (D-PCM) is the early member of PCM family, which only
includes the charge density of the solute wavefunction within the solute surface into
the solute–solvent interaction. The integral equation formalism PCM (IEF-PCM)
2 Computational Methods in Rh-Catalyzed C–H Functionalization
while most large enough basis sets can yield the same result in DFT calculations
[55]. Additionally, when the number of base functions for using a basis set is the
same, the time consuming can be saved by using a basis set with less Gaussian-type
function under the same precision [56]. Therefore, segmented contraction basis sets,
such as Pople’s basis sets and def2 series of basis sets, are the better choice in DFT
calculations [55, 57, 58].
For the computational study of Rh-catalyzed C–H functionalization, regular polarization functions are necessary, which can improve the accuracy to a great extent [59].
However, the larger angular momentum functions are unnecessary. A triple-zeta basis
set is usually slightly better than a double-zeta one [60, 61]. Followed this idea, 631G(d) is the smallest acceptable basis set for the description of the atoms except
for Rh metal in geometry optimizations [45, 62, 63]. The basis set of 6-311G(d,p) is
another better choice for both accuracy and efficiency [50, 64]. When def2 series of
basis set is used, def2-SVP is acceptable, while, def2-TZVP is a better one [65]. In
an anionic molecule, defuse functions are necessary, therefore, 6-31 + G(d) is the
acceptable basis set [44, 66]. To obtain accurate energy information, the polarization functions and defuse functions should be both taken into account in the energy
calculations. The first choice of basis set for the description of the atoms except for
Rh metal is 6-311 + G(d,p) followed by 6-31 + G(d) and 6-311G(d,p) in energy
calculations [63, 67–69].
For the DFT calculation onto Rh metal atom, employing a pseudo potential basis
set is strongly recommended for the consideration of both accuracy and efficiency.
In this area, LANL2DZ [70] is the smallest basis set for Rh metal atom, which only
provides only acceptable accuracy for some geometry optimizations and energy
calculations [62, 64, 67, 69]. The larger ones, such as SDD [71], LANL2TZ [70],
LANL08 [72], and LANL08(f) [73], are also recommended for Rh metal atom
[63, 68].
2.1.2 Solvent Effect
The solvent effect is crucial to Rh-catalyzed C–H functionalization, which should
always be considered in energy calculations. The solvent effect in homogeneous
catalysis calculations is considered by the implicit solvent model. In the implicit
solvent model, the solvent environment is simply considered as a polarizable continuous medium. The advantage of the implicit solvent model is that it can represent the
average effect of solvents without the consideration of various possible molecular
arrangements of solvent layer. The weakness is that the strong interaction between
solvent and solute cannot be represented, such as hydrogen bond. Moreover, the
accuracy of solvation energy for ionic solute cases is significantly lower than that of
neutral solute cases.
Dielectric formulation (D-PCM) is the early member of PCM family, which only
includes the charge density of the solute wavefunction within the solute surface into
the solute–solvent interaction. The integral equation formalism PCM (IEF-PCM)