Dear siesta users,
i am performing some tests in pi stacked complexes, small systems like the
benzene dimer. The problem that I am facing is that when I use LDA/DZP
methodology I find that the interaction between the perfect sandwich benzene
dimer (BBS) (two benzenes in perfect alingment) is repulsive by about 3
kcal/mol. I did the same test with the parallel displaced dimer BBPD ( two
parallel benzenes but one is slipped) and the interaction is again repulsive by
1.34 kcal/mol. The later values are BSSE corrected
However, when I computed the T shaped dimer, (two benzenes planes
perpendicular, an H atom is over one benzene) the interaction energy is
correcet, -2.8 kcal/mol close to the result obtained with gaussian03 and
SVWN5/6-31G* -3.1 kcal/mol. the results for other bezene dimers are correct.
The problem seems to be when the molecules are parallel. This is what I have
done:
1-changed r-cut of the pseudos from 1.25 to 1.5 no effect
2-the mesh cutoff = 200 Ry large enough...
3- I have performed the optimization including BSSE at each point. the results
are very far from the correct values. The BSSE optimized Eint are BBS atractive
by 0.35 kcal/mol and BBPD atractive by 0.6 kcal/mol. (the LDA plane wave
results obtaiend with abinit are 1 kcal/mol BBS and 2.6 kcal/mol)
4- changed the cell from 15x15x15 to 25x25x25.
5- I have changed from DZP to TZP, very small effect
Below is a sample input if someone one to check it, maybe I am doing something
weird in the input file...I am aware of the work by Tournus PRB72-165421 were
there are reported better values with siesta, BBS (Eint= 0.86kcal/mol) and BBPD
(Eint=2.19kcal/mol). He used DZP on carbon plus 3s orbitals and DZ for H. Any
help and suggestions will be very very welcome. I can´t believe that the
problem is only related with basis set...Many thanks
Regards,
Pablo
# FDF file for bb
# General System descriptors
SystemName bb # Descriptive name of the system
SystemLabel bb # Short name for naming files
NumberOfAtoms 24 # Number of atoms
NumberOfSpecies 4 # Number of species
%block Chemical_Species_Label
1 6 C
2 1 H
3 -6 C_G
4 -1 H_G
%endblock Chemical_Species_Label
PAO.BasisSize DZP
# Lattice, coordinates, k-sampling
LatticeConstant 15.0000 Ang
%block LatticeVectors
1.000000 0.000000 0.000000
0.000000 1.000000 0.000000
0.000000 0.000000 1.000000
%endblock LatticeVectors
%block kgrid_Monkhorst_Pack
1 0 0 0.0
0 1 0 0.0
0 0 1 0.0
%endblock kgrid_Monkhorst_Pack
AtomicCoordinatesFormat NotScaledCartesianAng # Format for coordinates
AtomicCoorFormatOut Ang
%block AtomicCoordinatesAndAtomicSpecies
0.00007541 1.39614453 -0.52224559 1 C 1
0.00005694 -1.39616257 -0.52244945 1 C 2
1.20856458 0.69783088 -0.52206605 1 C 3
1.20854870 -0.69785510 -0.52213672 1 C 4
-1.20859118 0.69793759 -0.52223820 1 C 5
-1.20859462 -0.69794943 -0.52230606 1 C 6
0.00001876 2.50301560 -0.51844121 2 H 7
0.00000234 -2.50298471 -0.51879817 2 H 8
2.16696010 1.25133637 -0.51844283 2 H 9
2.16695506 -1.25135399 -0.51859969 2 H 10
-2.16687661 1.25132301 -0.51874710 2 H 11
-2.16688016 -1.25129786 -0.51893443 2 H 12
0.00003837 1.39593676 2.71878371 3
0.00000867 -1.39596528 2.7190383 3
1.20863962 0.69782912 2.71919098 3
1.20862372 -0.69784522 2.719359330 3
-1.20867507 0.69788258 2.71928543 3
-1.20867995 -0.69785978 2.71944903 3
0.00001516 2.50291968 2.71281822 4
-0.00002612 -2.50292522 2.71336602 4
2.16690307 1.25126250 2.71416119 4
2.16688841 -1.25131130 2.71442735 4
-2.16686093 1.25127459 2.71433044 4
-2.16688713 -1.25125767 2.71460809 4
%endblock AtomicCoordinatesAndAtomicSpecies
# DFT, Grid, SCF
XC.functional LDA # Exchange-correlation functional type
XC.authors CA # Particular parametrization of xc func
SpinPolarized .false. # Spin unpolarized calculation
MeshCutoff 200. Ry # Equivalent planewave cutoff for the grid
MaxSCFIterations 450 # Maximum number of SCF iterations per step
DM.MixingWeight 0.3 # New DM amount for next SCF cycle
DM.Tolerance 1.d-6 # Tolerance in maximum difference
# between input and output DM
DM.NumberPulay 3 # Number of SCF steps between pulay mixing
