TY - JOUR
T1 - The structures, binding energies and vibrational frequencies of Ca3 and Ca4 - An application of the CCSD(T) method
AU - Lee, Timothy J.
AU - Rendell, Alistair P.
AU - Taylor, Peter R.
PY - 1992/1/1
Y1 - 1992/1/1
N2 - The Ca3 and Ca4 metallic clusters have been investigated using state-of-the-art ab initio quantum mechanical methods. Large atomic natural orbital basis sets have been used in conjunction with the singles and doubles coupled-cluster (CCSD) method, a coupled-cluster method that includes a perturbational estimate of connected triple excitations, denoted CCSD(T), and the multireference configuration interaction (MRCI) method. The equilibrium geometries, binding energies and harmonic vibrational frequencies have been determined with each of the methods so that the accuracy of the coupled-cluster methods may be assessed. Since the CCSD(T) method reproduces the MRCI results very well, cubic and quartic force fields of Ca3 and Ca4 have been determined using this approach and used to evaluate the fundamental vibrational frequencies. The infrared intensities of both the e′ mode of Ca3 and the t2 mode of Ca4 are found to be small. The results obtained in this study are compared and contrasted with those from our earlier studies on small Be and Mg clusters.
AB - The Ca3 and Ca4 metallic clusters have been investigated using state-of-the-art ab initio quantum mechanical methods. Large atomic natural orbital basis sets have been used in conjunction with the singles and doubles coupled-cluster (CCSD) method, a coupled-cluster method that includes a perturbational estimate of connected triple excitations, denoted CCSD(T), and the multireference configuration interaction (MRCI) method. The equilibrium geometries, binding energies and harmonic vibrational frequencies have been determined with each of the methods so that the accuracy of the coupled-cluster methods may be assessed. Since the CCSD(T) method reproduces the MRCI results very well, cubic and quartic force fields of Ca3 and Ca4 have been determined using this approach and used to evaluate the fundamental vibrational frequencies. The infrared intensities of both the e′ mode of Ca3 and the t2 mode of Ca4 are found to be small. The results obtained in this study are compared and contrasted with those from our earlier studies on small Be and Mg clusters.
KW - Ca/Ca metallic clusters
KW - CCSD(T) method
KW - Vibrational frequencies
UR - http://www.scopus.com/inward/record.url?scp=0000084168&partnerID=8YFLogxK
U2 - 10.1007/BF01113249
DO - 10.1007/BF01113249
M3 - Article
AN - SCOPUS:0000084168
VL - 83
SP - 165
EP - 175
JO - Theoretica Chimica Acta
JF - Theoretica Chimica Acta
SN - 0040-5744
IS - 1-2
ER -