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Approximate inclusion of four-mode couplings in vibrational coupled-cluster theory
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10.1063/1.4721626
/content/aip/journal/jcp/136/20/10.1063/1.4721626
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/20/10.1063/1.4721626

Figures

Image of FIG. 1.
FIG. 1.

Errors of different wave function methods for the fundamentals (a), overtones (b), and combinations (c), when up to four-mode couplings are included in the Hamiltonian. Each point represents a state, the position of the points is corresponding to the state density. Superimposed is a boxplot giving the mean value, 25% and 75% quartiles, and the value range of all the samples. Statistical outliers lay over the upper whisker.

Image of FIG. 2.
FIG. 2.

Errors of different wave function methods for the “simple” (a), “medium” (b), and “hard” (c) category, when up to four-mode couplings are included in the Hamiltonian, see Fig. 1 for details.

Image of FIG. 3.
FIG. 3.

With positive sign: VCC[3] IR spectrum of HOCN at the four-mode coupling level. With negative sign: VCI[6] IR spectrum of HOCN at the four-mode coupling level for comparison. In the inset: enlarged view of the 3000–4000 cm−1 region.

Image of FIG. 4.
FIG. 4.

With positive sign: VCC[3pt4] IR spectrum of HOCN at the four-mode coupling level. With negative sign: VCI[6] IR spectrum of HOCN at the four-mode coupling level for comparison. In the inset: enlarged view of the 3000–4000 cm−1 region.

Image of FIG. 5.
FIG. 5.

With positive sign: VCC[3pt4F] IR spectrum of HOCN at the four-mode coupling level. With negative sign: VCI[6] IR spectrum of HOCN at the four-mode coupling level for comparison. In the inset: enlarged view of the 3000–4000 cm−1 region.

Image of FIG. 6.
FIG. 6.

With positive sign: VCC[4] IR spectrum of HOCN at the four-mode coupling level. With negative sign: VCI[6] IR spectrum of HOCN at the four-mode coupling level for comparison. In the inset: enlarged view of the 3000–4000 cm−1 region.

Tables

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Table I.

The orders in the fluctuation operator to which the amplitudes and the energy are correct for different VCC models. In the last column is reported the order in which each amplitudes enter.

Generic image for table
Table II.

Computational scaling of different VCC models depending on the level of the Hamiltonian operator.

Generic image for table
Table III.

Orders to which response excitation energies are correct in different VCC models.

Generic image for table
Table IV.

Mean and maximum errors for the transition energies relative to fundamentals, overtones, and combinations of the five tetra-atomic molecules considered, with respect to the VCI[6] results. Data in cm−1.

Generic image for table
Table V.

Results of the paired Student's T test on the data for fundamentals and combinations for the different wave function methods and Hamiltonians. Non-significant values are shown in bold, NA test not performed.

Generic image for table
Table VI.

Mean and maximum errors for the transition energies in the “simple,” “medium,” and “hard” class of states (see text) of the five tetra-atomic molecules considered, with respect to the VCI[6] results. Data in cm−1.

Generic image for table
Table VII.

Results of the paired Student's T test on the data in the “simple” and “medium” categories for the different wave function methods and Hamiltonians. Non-significant values are shown in bold, NA test not performed.

Generic image for table
Table VIII.

Errors of VCC[3], VCC[3pt4], and VCC[3pt4F] methods, with respect to the VCC[4] method (cm−1) for the fundamentals and selected overtones of dioxirane.

Generic image for table
Table IX.

Fundamental excitation energies (cm−1) for ethylene oxide along with some important resonances. VCC[3], VCC[2pt3], and VCC[3pt4] energies are relative to VCC[4]. The VCC[4] summed singles weights are also shown.

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/content/aip/journal/jcp/136/20/10.1063/1.4721626
2012-05-31
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Approximate inclusion of four-mode couplings in vibrational coupled-cluster theory
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/20/10.1063/1.4721626
10.1063/1.4721626
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