Small Be Clusters



Be3 Bond Lengths and Binding Energies


Method Basis re (ao) De(kcal/mol)
SCF[4s 2p 1d](4.472)a-3.2
CISD+Q[4s 2p 1d](4.472)8.9
CCSD[4s 2p 1d]4.4724.2
CPF[4s 2p 1d]4.4888.6
MCSCF[4s 2p 1d](4.372)-2.3
MCRI[4s 2p 1d]4.37314.2
SCF[5s 3p 12d 1f](4.240)-1.4
CCSD[5s 3p 12d 1f]4.24011.3
CPF[5s 3p 12d 1f]4.20214.9
MCSCF[5s 3p 12d 1f](4.199).2
MCRI[5s 3p 12d 1f]4.19922.4
a Bond lengths in parentheses were not optimized.

Observations

Small Be Clusters

Be4 Binding Energies

MethodBasisDe(kcal/mol)
SCF[4s 2p 1d]32.9
CCSD[4s 2p 1d]42.9
MCSCF[4s 2p 1d]34.9
MCRI[4s 2p 1d]56.1
SCF[5s 3p 2d 1f]40.0
CCSD[5s 3p 2d 1f]63.5
CASSCF[5s 3p 2d 1f]45.0
MCRI[5s 3p 2d 1f]77.3
a Bond length fixed at 3.9ao.

Observations

CCSD(T) Results

Be3 and Be4

Be3
MethodBasisre (ao)De(lcal/mol
CCSD[5s 3p 2d 1f]4.23911.3
CCSD(T)[5s 3p 2d 1f]4.231720.4
CMCRI[5s 3p 2d 1f]4.230022.5
Be4
CCSD[4s 2p 1d]4.04144.2
CCSD(T)[4s 2p 1d]4.06058.5
MCRI[4s 2p 1d]4.05459.2
CCSD[5s 3p 2d 1f]43.90063.5
CCSD(T)[5s 3p 2d 1f]3.92179.5
CCSD(T) performs remarkably well for these sytems!

Small Be Clusters: CCSD(T) Calculations

Be3 and Be4 Vibrations(a)



MethodBasisa' modee'mode
CCSD[5s 3p 2d 1f]433407
MCRI[5s 3p 2d 1f]490427
CCSD(T)[5s 3p 2d 1f]480417
CCSD(T)b[5s 3p 2d 1f]459400
MethodBasisa' modee'modet2 mode
CCSD[4s 2p 1d]597445534
MCRI[4s 2p 1d]602451529
CCSD(T)[4s 2p 1d]602436527
CCSD[5s 3p 2d 1f]667480581
CCSD(T)[5s 3p 2d 1f]662469571
CCSD(T)b[5s 3p 2d 1f]639455682
(a)Harmonic frequency unless otherwise indicated.
(b)Fundamental frequency.

Observations

Structure of C3+

C3+ DZP Basis Results

Cyclic/ Linear Separation (kcal/mol)

MethodSeparation
MCSCF1.46
MCRI1.68
CISD15.69
QCISD9.38
QCISD(T).87
MP4(SDTQ)-24.63

Observations

C3+ Extended Basis Results

[5s 3p 2d 1f] Cyclic/Linear Separation (kcal/mol)

MethodSeparation
MCSCF3.18
MCRI5.18
QCISD12.62
QCISD(T)3.42

Structure of C3+

C20

C20 results

C20 relative energies (eV)

LDA optimized geometries
Methodfullereneflakering
SCF0.-2.0-2.2
LDA0.1.13.3
MP20.1.12.8
CCSD0.-0.60.9
CCSD(T)0.-0.01.7
Best estimate0.0.73.0
SCF optimized geometries
Methodfullereneflakering
SCF0.-2.5-3.4
LDA0.1.03.8
DFT0.-2.3-3.4
MP20.0.83.9
CCSD0.-1.2-0.9
CCSD(T)0.-0.6-2.2
Best estimate0.0.54.1