Table 2. Only Cases within the Set of 1501 Benchmark Frequencies with CMA-0A[CCSD(T)/cc-pVTZ, MP2/cc-pVTZ] Residuals (ϵ, cm–1) Greater than 1.5 cm–1 in Magnitude, Together with the Corresponding CMA-1A and CMA-2A Results That Target These Outliers.
| Molecule and mode | Description | Benchmark | ϵ[CMA-0A] | ϵ[CMA-1A(1)] | ϵ[CMA-2A](n)a | ηb (%) |
|---|---|---|---|---|---|---|
| nitrous oxide, ω3(σ) | sym. stretch | 1297.09 | 9.34 | 0.00 | 0.00 (1) | 25 |
| ketene, ω9(b2) | C=C=O bend | 514.86 | 7.12 | 0.00 | 0.00 (2) | 22 |
| ketene, ω8(b2) | CH2 wag | 584.48 | –6.28 | 0.00 | 0.00 (2) | 22 |
| nitrous oxide, ω1(σ) | antisym. stretch | 2282.57 | –5.33 | 0.00 | 0.00 (1) | 25 |
| benzene, ω18(b1u) | ring def. | 1158.88 | 4.90 | 0.00 | 0.00 (10) | 36 |
| benzene, ω17(b1u) | ring def. | 1328.17 | –4.29 | 0.00 | 0.00 (10) | 36 |
| spiropentane, ω4(a1) | ring breathing | 1054.41 | 3.67 | 0.00 | 0.03 (7) | 21 |
| spiropentane, ω3(a1) | sym. CH2 wag | 1076.02 | –3.60 | 0.01 | 0.01 (7) | 21 |
| methyl nitrite, ω12(a) | N–O stretch | 595.01 | 3.55 | 0.68 | –0.12 (9) | 60 |
| nitromethane, ω4(a) | NO2 rock | 1642.57 | –2.87 | –1.11 | 0.04 (13) | 87 |
| nitromethane, ω10(a) | CH3 rock | 1110.76 | 2.71 | 0.12 | 0.12 (13) | 87 |
| n–butane, ω28(bu) | CH3 stretch | 3028.05 | 1.81 | 0.00 | 1.81 (10) | 28 |
| n–butane, ω29(bu) | CH2 stretch | 3023.91 | –1.79 | –0.03 | –1.79 (10) | 28 |
| aziridine, ω1(a′) | CH2 rock | 783.89 | 1.76 | 1.19 | 1.11 (12) | 67 |
| isobutane, ω3(a1) | CH stretch | 3019.64 | 1.62 | 0.02 | 1.62 (5) | 14 |
| isobutane, ω2(a1) | CH3 sym. stretch | 3024.21 | –1.56 | 0.04 | –1.56 (5) | 14 |
a
n = the number of off-diagonal elements included for the ξ = 0.020 cutoff.
b
η = number of FCMA(A) off-diagonal elements included as a percentage of the vibrational degrees of freedom for the given molecule.