# Sample input files¶

## Water SCF calculation and geometry optimization in a 6-31g basis¶

The Getting Started input file performs a geometry optimization in a single task. A single point SCF energy calculation is performed and then restarted to perform the optimization (both could of course be performed in a single task).

### Job 1. Single point SCF energy¶

 start h2o
title "Water in 6-31g basis set"

geometry units au
O      0.00000000    0.00000000    0.00000000
H      0.00000000    1.43042809   -1.10715266
H      0.00000000   -1.43042809   -1.10715266
end
basis
H library 6-31g
O library 6-31g
end


The final energy should be -75.983998.

### Job 2. Restarting and perform a geometry optimization¶

 restart h2o
title "Water geometry optimization"



There is no need to specify anything that has not changed from the previous input deck, though it will do no harm to repeat it.

## Compute the polarizability of Ne using finite field¶

### Job 1. Compute the atomic energy¶

 start ne
title "Neon"
geometry; ne 0 0 0; end
basis spherical
ne library aug-cc-pvdz
end
scf; thresh 1e-10; end


The final energy should be -128.496350.

### Job 2. Compute the energy with applied field¶

An external field may be simulated with point charges. The charges here apply a field of magnitude 0.01 atomic units to the atom at the origin. Since the basis functions have not been reordered by the additional centers we can also restart from the previous vectors, which is the default for a restart job.

 restart ne
title "Neon in electric field"
geometry units atomic
bq1 0 0 100 charge 50
ne  0 0 0
bq2 0 0 -100 charge -50
end


The final energy should be -128.496441, which together with the previous field-free result yields an estimate for the polarizability of 1.83 atomic units. Note that by default NWChem does not include the interaction between the two point charges in the total energy.

## SCF energy of H2CO using ECPs for C and O¶

The following will compute the SCF energy for formaldehyde with ECPs on the Carbon and Oxygen centers.

title "formaldehyde ECP deck"

start ecpchho

geometry units au
C         0.000000  0.000000 -1.025176
O         0.000000  0.000000  1.280289
H         0.000000  1.767475 -2.045628
H         0.000000 -1.767475 -2.045628
end

basis
C  SP
0.1675097360D+02 -0.7812840500D-01  0.3088908800D-01
0.2888377460D+01 -0.3741108860D+00  0.2645728130D+00
0.6904575040D+00  0.1229059640D+01  0.8225024920D+00
C  SP
0.1813976910D+00  0.1000000000D+01  0.1000000000D+01
C  D
0.8000000000D+00  0.1000000000D+01
C  F
0.1000000000D+01  0.1000000000D+01
O  SP
0.1842936330D+02 -0.1218775590D+00  0.5975796600D-01
0.4047420810D+01 -0.1962142380D+00  0.3267825930D+00
0.1093836980D+01  0.1156987900D+01  0.7484058930D+00
O  SP
0.2906290230D+00  0.1000000000D+01  0.1000000000D+01
O  D
0.8000000000D+00  0.1000000000D+01
O  F
0.1100000000D+01  0.1000000000D+01
H  S
0.1873113696D+02  0.3349460434D-01
0.2825394365D+01  0.2347269535D+00
0.6401216923D+00  0.8137573262D+00
H  S
0.1612777588D+00  0.1000000000D+01
end

ecp
C nelec 2
C ul
1       80.0000000       -1.60000000
1       30.0000000       -0.40000000
2        0.5498205       -0.03990210
C s
0        0.7374760        0.63810832
0      135.2354832       11.00916230
2        8.5605569       20.13797020
C p
2       10.6863587       -3.24684280
2       23.4979897        0.78505765
O nelec 2
O ul
1       80.0000000       -1.60000000
1       30.0000000       -0.40000000
2        1.0953760       -0.06623814
O s
0        0.9212952        0.39552179
0       28.6481971        2.51654843
2        9.3033500       17.04478500
O p
2       52.3427019       27.97790770
2       30.7220233      -16.49630500
end

scf
vectors input hcore
maxiter 20
end



This should produce the following output:

      Final RHF  results
------------------

Total SCF energy =    -22.507927218024
One electron energy =    -71.508730162974
Two electron energy =     31.201960019808
Nuclear repulsion energy =     17.798842925142


## MP2 optimization and CCSD(T) on nitrogen¶

The following performs an MP2 geometry optimization followed by a CCSD(T) energy evaluation at the converged geometry. A Dunning correlation-consistent triple-zeta basis is used. The default of Cartesian basis functions must be overridden using the keyword spherical on the BASIS directive. The 1s core orbitals are frozen in both the MP2 and coupled-cluster calculations (note that these must separately specified). The final MP2 energy is -109.383276, and the CCSD(T) energy is -109.399662.

start n2

geometry
symmetry d2h
n 0 0 0.542
end

basis spherical
n library cc-pvtz
end

mp2
freeze core
end