| 11:48:42 AM PDT - Thu, Oct 24th 2013 |
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I am wondering functions of nwchem to add finite field to a calculation like Gaussian,
Gaussian : Field
DESCRIPTION
The Field keyword requests that a finite field be added to a calculation. In Gaussian 09, the field can either involve electric multipoles (through hexadecapoles) or a Fermi contact term. Field requires a parameter in one of these two formats: M±N or F(M)N, where M designates a multipole, and F(M) designates a Fermi contact perturbation for atom M (following the ordering in the molecule specification section of the input file). N*0.0001 specifies the magnitude of the field in atomic units in the first format, and specifies the magnitude of the Fermi contact perturbation in the second format.
Thus, Field=X+10 applies an electric dipole field in the X direction of 0.001 au, while Field=XXYZ-20 applies the indicated hexadecapole field with magnitude 0.0020 au and direction opposite to the default (which is determined by the standard orientation). Similarly, Field=F(3)27 applies a perturbation of 0.0027 times the spin density on atom 3.
I found following in the nwchem manual,
External electrostatic field
field <real xfield> [freq <real xffreq>] [vector <real xfvect(1:3)>]
Specifies an external electrostatic field, where <xfield> is the field strength, <xffreq> is the frequency in MHz and <xfvect> is the external field vector.
just want to clarify with few example,
1. unit of the field?
2. For static field just set freq to 0 ? To simulate optical excitation, we set xffreq to whatever THz number in unit of MHz?
3. For z axis field set vector 0 0 1 or 0 0 -1 ?
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