^{1,a)}

### Abstract

The accurate ground-state potential energy surface of lithium monohydroxide (LiOH) has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. Results obtained with the conventional and explicitly correlated coupled-cluster methods were compared. The higher-order electron correlation, scalar relativistic, and adiabatic effects were taken into account. The vibration-rotation energy levels of the LiOH, LiOD, Li18OH, and 6LiOH isotopologues were predicted to near “spectroscopic” accuracy.

I. INTRODUCTION

II. METHOD OF CALCULATION

III. RESULTS AND DISCUSSION

### Key Topics

- Lithium
- 24.0
- Potential energy surfaces
- 22.0
- Basis sets
- 20.0
- Rotation constants
- 15.0
- Ground states
- 11.0

## Figures

The total energy of LiOH (solid line) and LiOLi (dashed line) as a function of the valence angle LiOX (X=H, Li), calculated for the fixed equilibrium LiO and OH bond lengths. The functions are drawn to a common scale. Location of the ground and first excited states of the LiOX bending mode ν2 is shown schematically.

The total energy of LiOH (solid line) and LiOLi (dashed line) as a function of the valence angle LiOX (X=H, Li), calculated for the fixed equilibrium LiO and OH bond lengths. The functions are drawn to a common scale. Location of the ground and first excited states of the LiOX bending mode ν2 is shown schematically.

Natural atomic charges (in e) for the equilibrium configuration of LiOH and LiOLi, calculated using the HF/MP2 method with the aug-cc-pCVTZ basis set.

Natural atomic charges (in e) for the equilibrium configuration of LiOH and LiOLi, calculated using the HF/MP2 method with the aug-cc-pCVTZ basis set.

The total energy of LiOH as a function of the valence angle LiOH, calculated for the fixed equilibrium LiO and OH bond lengths using the HF (circles) and CCSD(T) (diamonds) methods, both with the aug-cc-pCV6Z basis set. The functions are drawn to a common scale. The function illustrating the classical electrostatic interaction energy (dashed line) is given for a comparison, see the text.

The total energy of LiOH as a function of the valence angle LiOH, calculated for the fixed equilibrium LiO and OH bond lengths using the HF (circles) and CCSD(T) (diamonds) methods, both with the aug-cc-pCV6Z basis set. The functions are drawn to a common scale. The function illustrating the classical electrostatic interaction energy (dashed line) is given for a comparison, see the text.

## Tables

Molecular parameters for the X 1Σ+ state of LiOH determined at the CCSD(T)/aug-cc-pCVnZ level of theory.

Molecular parameters for the X 1Σ+ state of LiOH determined at the CCSD(T)/aug-cc-pCVnZ level of theory.

Molecular parameters a for the X 1Σ+ state of LiOH determined at the CCSD(T)-F12b/cc-pCVnZ-F12 level of theory.

Molecular parameters a for the X 1Σ+ state of LiOH determined at the CCSD(T)-F12b/cc-pCVnZ-F12 level of theory.

Molecular parameters a for the X 1Σ+ state of LiOH determined using various potential energy surfaces.

Molecular parameters a for the X 1Σ+ state of LiOH determined using various potential energy surfaces.

Vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of LiOH.

Vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of LiOH.

Vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of LiOD.

Vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of LiOD.

Calculated vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of Li18OH.

Calculated vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of Li18OH.

Calculated vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of 6LiOH.

Calculated vibrational term values T (in cm−1) and the effective rotational B and quartic centrifugal distortion D constants (in MHz) for the X 1Σ+ state of 6LiOH.

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