How to use semiempirical methods?


Just Got Here

Hi all, is my first post, they could help with the following.


They could explain how to use semiempirical methods in NWChem?
Currently I am working with organic molecules, and want to use these methods to calculate UV-Vis.
But I want to use the best semiempirical methods. How could I write my input file to calculate for example, this molecule of chalcone:

30

C -6.47890 9.19635 -0.91987
C -7.56567 9.35930 -1.78507
C -5.19982 8.93517 -1.43065
C -7.38671 9.27195 -3.16732
C -5.03361 8.88165 -2.81671
C -6.11665 9.03677 -3.69299
H -6.63333 9.27107 0.15620
H -8.55536 9.55799 -1.37738
H -8.23777 9.40162 -3.83331
H -5.97730 8.99028 -4.77129
C -4.10904 8.74269 -0.45031
C -3.27901 7.51651 -0.58293
O -3.98238 9.53613 0.47405
C -2.17251 7.38583 0.16359
H -3.60071 6.74305 -1.27008
C -1.29216 6.21171 0.11182
H -1.88787 8.16462 0.86975
C -0.97861 5.56348 -1.09059
C -0.70056 5.75799 1.29773
C -0.11493 4.46496 -1.10029
C 0.45260 4.01160 0.08865
C 0.16289 4.65974 1.28729
H -1.38715 5.91296 -2.03605
H 0.12100 3.96991 -2.03882
H 1.12700 3.15934 0.07970
H 0.61129 4.31396 2.21502
H -0.91221 6.25301 2.24319
N -3.72185 8.71145 -3.39830
O -2.88362 9.59150 -3.17594
O -3.54279 7.69198 -4.07715
_____________________________________

Currently my input files for DFT calculation are as follows:

echo

start H2

memory 12000 mb heap 4000 mb stack 4000 mb

title "Title"
charge 0

geometry units angstroms print
load format xyz H2.xyz
end

basis
 * library 6-31G*
end

dft
 xc b3lyp
mult 1
end

driver
 maxiter 200
xyz o-nch
end

task dft optimize
title "Frequency"
task dft freq
_______________________________________

I appreciate your fast response.

Daniel


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