Geometry optimization
The most important calculation in all calculation is to find the minimum energy
configuration of a system. From here he can start to do all the other properties we
want to calculate.
ORCA is a very intuitive program and you just need some knowledge in DFT theory to
start using this code.
Let's find the bond length for the hydrogen molecule. First you have to specify
which theory the code is going to use. In this tutorial we will only use DFT.
Then you have to specify the type of coordinates you will use: XYZ type or Internal
coordinates.
Specifying KS keyword allows you to use DFT.
RKS or UKS
RKS: Restricted Kohn Sham for closed shell systems.
UKS: Unrestricted Kohn Sham for open shell systems.
XC functional Functional to calculate the
exchange correlation energy:
PBE, B3LYP, PW91, RPBE, TPSS0, M06, M062x etc...
Opt Default Single Point. Indicates a
geometry optimization calculation.
NumFreq Numerical Derivatives. Alternative AnFreq
that calculates the faster analytical frequencies but no the dipole changes.
[emma@pople]$ vi geom_opt.inp
#ORCA Basic Input DFT calculation
! RKS PBE TZVP
! PMODEL #Initial density guess
! XYZfile #Type of coordinates
! TightSCF #SCF convergence criteria
! PAL8 #Number of core processors
! Opt #Geometry optimization
! NumFreq #Numerical Frequency
! NumFreq #Vibrational analysis.
%method
Grid 2 #110 grid points for the SCF
FinalGrid 4 #302 grid points
end
#Type Charge Multiplicity
* xyz 0 1
H 0.0 0.0 0.5
H 0.0 0.0 0.5
*
[emma@pople]$/path/to/orca geom_opt.inp
Alternative for torque users
[emma@pople]$qsub geom_opt.inp
FamaLab tutorial