I am trying to understand how exactly the NOSCF keyword works. I have run a simple example involving 2 Hydrogen molecules: first i run an SCF calculation on each molecule separately, saving movecs files, and then i run a NOSCF calculation on the dimer with input guess the fragment movecs files from the previous step:
title "H2 dimer"
start H2
echo
geometry "mol1" units angstroms noautosym nocenter noautoz
H 0.000 0.000 0.000
H 0.740 0.000 0.000
end
geometry "mol2" units angstroms noautosym nocenter noautoz
H 0.000 0.000 2.000
H 0.740 0.000 2.000
end
geometry "dimer" units angstroms noautosym nocenter noautoz
H 0.000 0.000 0.000
H 0.740 0.000 0.000
H 0.000 0.000 2.000
H 0.740 0.000 2.000
end
BASIS spherical
* library sto-2g
END
set geometry "mol1"
scf
vectors input atomic output "mol1.movecs"
end
task scf energy
set geometry "mol2"
scf
vectors input atomic output "mol2.movecs"
end
task scf energy
set geometry "dimer"
scf
vectors input fragment "mol1.movecs" "mol2.movecs" output "dimer.movecs"
noscf
end
task scf energy
I have converted the movecs files to ASCII:
mol1
NSets: 1
NBF: 2
nmo: 2
Occupation numbers: 0.2000E+01 0.0000E+00
Eigenvalues: -0.5675E+00 0.6849E+00
Eigenvectors: 0.5490E+00 0.5490E+00
Eigenvectors: 0.1211E+01-0.1211E+01
Energy =-0.1093E+01 Enrep = 0.7151E+00
mol2
NSets: 1
NBF: 2
nmo: 2
Occupation numbers: 0.2000E+01 0.0000E+00
Eigenvalues: -0.5675E+00 0.6849E+00
Eigenvectors: 0.5490E+00 0.5490E+00
Eigenvectors: 0.1211E+01-0.1211E+01
Energy =-0.1093E+01 Enrep = 0.7151E+00
NSets: 1
NBF: 4
nmo: 4
Occupation numbers: 0.2000E+01 0.2000E+01 0.0000E+00 0.0000E+00
Eigenvalues: -0.5675E+00-0.5675E+00 0.6849E+00 0.6849E+00
Eigenvectors: 0.5490E+00 0.5490E+00 0.0000E+00 0.0000E+00
Eigenvectors: -0.6392E-01-0.6392E-01 0.5527E+00 0.5527E+00
Eigenvectors: 0.1211E+01-0.1211E+01 0.3835E-17 0.3835E-17
Eigenvectors: -0.8719E-01 0.8719E-01 0.1214E+01-0.1214E+01
Energy =-0.2174E+01 Enrep = 0.2456E+01
Eigenvalues of the dimer are exactly the eigenvalues of the 2 molecules sorted. The first dimer's eigenvector coefficients are the 2 coefficients of the first eigenvector of mol1 padded with 2 0s. I do not understand how the other 3 eigenvectors are produced though. Is the basis of the dimer produced by concatenating the basis sets of the 2 molecules?
Thanks for any suggestions,
Kostas
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