DIPOLE MOMENT for a vacuum molecule
Posted: Fri Dec 18, 2009 4:12 pm
Dear All,
I am trying to calculate the dipole moment for the thio-oxalic molecule
(COOH-COSH) in vacuum. I am interested in this quantity because
it can be compared with the value obtained in the Stark effect experiments. Also
I am interested in the dipole moment value as I want to calculate the IR
intensities for the molecule in vacuum.
The problem I get into is that depending on the position of the molecule in the supercell I obtained very different values for the dipole moment. Thus, for a certain position of the molecule in the supercell I obtain a dipole moment with the components:
dipolmoment -21.047999 0.103052 -0.040473 electrons x Angstroem
while for another position of the molecule in the supercell (obtained via a translation process) I obtain a dipole moment with the components:
dipolmoment -0.083514 158.217590 -0.162468 electrons x Angstroem
The total energy for the two runs is also very different: -45.61 eV in the first
case and + 105.33 eV in the second case (there is no typo in the sign of the
second value. It is +). Nevertheless the total energy without the dipole
correction is identical(-48.33 eV). As well as the geometries.
Thus, while I have identical total energies (without dipole correction) and structures, I obtain very different values for the dipole moment values.
To get the value for the dipole moment I use the following INCAR (irrespective of the position of the molecule in the supercell):
###############################################################
ISTART = 2 ! WAVECAR available
ICHARG = 1 ! readed from CHGCAR
ENCUT = 550 ! cut off energy
PREC = High ! precision high
ISPIN = 1 ! non-spin polarized calculation
ISIF = 2 ! calculate stress tensor
ISYM = 2 ! sym ON save memory
IDIPOL = 4 ! dipol moment in all directions
EDIFF = 5e-7 ! stopping crit for electr min
NELM = 100 !
NELMIN = 5 ! minimum 5 electronic steps
IALGO = 48 !
EDIFFG = -0.002571 ! stopping crit for ions
NSW = 70 ! 70 ionic steps
POTIM = 0.0052918 !
IBRION = 2 ! K conjugate gradient for ions
ISMEAR = 0 ! Gaussian smearing
SIGMA = 0.11 ! broadening should be ok
LCHARG = TRUE ! write CHGCAR CHG files
LWAVE = TRUE ! write WAVECAR file
LREAL = Auto ! proj op eval in real sp
LPLANE = TRUE !
NPAR = 32 !
###############################################################
The POSCARs for the two runs (for which I gave before the dipole moment values) are:
POSCAR 1
###############################################################
cpTpc rot O db S adapted
1.00000000000000000
17.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 17.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 17.0000000000000000
2 3 2 1
Selective dynamics
Direct
0.5018594318805619 0.6165219912144694 0.5728165345034969 T T T
0.4997975596824178 0.6167547684692719 0.6630018695800838 T T T
0.5770024023565359 0.6161315301586152 0.5452774027543809 T T T
0.4313257908910161 0.5854748552589901 0.6875783244729147 T T T
0.4432559540856101 0.6177049698882507 0.5326433212975495 T T T
0.5721554963612641 0.6176321725641040 0.4877098191261964 T T T
0.4319824855625128 0.5898136934269681 0.7453321290021732 T T T
0.5674508791800688 0.6538107249016839 0.7201517757337862 T T T
###############################################################
POSCAR 2
###############################################################
cpTpc rot O db S adapted
1.00000000000000000
17.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 17.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 17.0000000000000000
2 3 2 1
Selective dynamics
Direct
0.5017764705882328 0.4985823529411775 0.4551723529411760 T T T
0.4996752941176439 0.4990664705882324 0.5453170588235281 T T T
0.5769923529411756 0.4989835294117668 0.4277070588235290 T T T
0.4311264705882323 0.4682217647058806 0.5701882352941183 T T T
0.4433052941176499 0.4992605882352947 0.4148052941176488 T T T
0.5721194117647030 0.5001641176470599 0.3701200000000000 T T T
0.4320752941176451 0.4726094117647079 0.6279252941176452 T T T
0.5677594117647047 0.5357800000000026 0.6020994117647049 T T T
###############################################################
As k-point I am using the Gamma point as I am dealing with a single molecule in a big box.
I would be very grateful is someone could help with an advice on how to properly obtain the values for the dipole moments. According to the manual and to the forum the IDIPOL = 4 setting should be sufficient for a vacuum molecule. Have I missed something ?
With all my best wishes,
Eduard
I am trying to calculate the dipole moment for the thio-oxalic molecule
(COOH-COSH) in vacuum. I am interested in this quantity because
it can be compared with the value obtained in the Stark effect experiments. Also
I am interested in the dipole moment value as I want to calculate the IR
intensities for the molecule in vacuum.
The problem I get into is that depending on the position of the molecule in the supercell I obtained very different values for the dipole moment. Thus, for a certain position of the molecule in the supercell I obtain a dipole moment with the components:
dipolmoment -21.047999 0.103052 -0.040473 electrons x Angstroem
while for another position of the molecule in the supercell (obtained via a translation process) I obtain a dipole moment with the components:
dipolmoment -0.083514 158.217590 -0.162468 electrons x Angstroem
The total energy for the two runs is also very different: -45.61 eV in the first
case and + 105.33 eV in the second case (there is no typo in the sign of the
second value. It is +). Nevertheless the total energy without the dipole
correction is identical(-48.33 eV). As well as the geometries.
Thus, while I have identical total energies (without dipole correction) and structures, I obtain very different values for the dipole moment values.
To get the value for the dipole moment I use the following INCAR (irrespective of the position of the molecule in the supercell):
###############################################################
ISTART = 2 ! WAVECAR available
ICHARG = 1 ! readed from CHGCAR
ENCUT = 550 ! cut off energy
PREC = High ! precision high
ISPIN = 1 ! non-spin polarized calculation
ISIF = 2 ! calculate stress tensor
ISYM = 2 ! sym ON save memory
IDIPOL = 4 ! dipol moment in all directions
EDIFF = 5e-7 ! stopping crit for electr min
NELM = 100 !
NELMIN = 5 ! minimum 5 electronic steps
IALGO = 48 !
EDIFFG = -0.002571 ! stopping crit for ions
NSW = 70 ! 70 ionic steps
POTIM = 0.0052918 !
IBRION = 2 ! K conjugate gradient for ions
ISMEAR = 0 ! Gaussian smearing
SIGMA = 0.11 ! broadening should be ok
LCHARG = TRUE ! write CHGCAR CHG files
LWAVE = TRUE ! write WAVECAR file
LREAL = Auto ! proj op eval in real sp
LPLANE = TRUE !
NPAR = 32 !
###############################################################
The POSCARs for the two runs (for which I gave before the dipole moment values) are:
POSCAR 1
###############################################################
cpTpc rot O db S adapted
1.00000000000000000
17.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 17.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 17.0000000000000000
2 3 2 1
Selective dynamics
Direct
0.5018594318805619 0.6165219912144694 0.5728165345034969 T T T
0.4997975596824178 0.6167547684692719 0.6630018695800838 T T T
0.5770024023565359 0.6161315301586152 0.5452774027543809 T T T
0.4313257908910161 0.5854748552589901 0.6875783244729147 T T T
0.4432559540856101 0.6177049698882507 0.5326433212975495 T T T
0.5721554963612641 0.6176321725641040 0.4877098191261964 T T T
0.4319824855625128 0.5898136934269681 0.7453321290021732 T T T
0.5674508791800688 0.6538107249016839 0.7201517757337862 T T T
###############################################################
POSCAR 2
###############################################################
cpTpc rot O db S adapted
1.00000000000000000
17.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 17.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 17.0000000000000000
2 3 2 1
Selective dynamics
Direct
0.5017764705882328 0.4985823529411775 0.4551723529411760 T T T
0.4996752941176439 0.4990664705882324 0.5453170588235281 T T T
0.5769923529411756 0.4989835294117668 0.4277070588235290 T T T
0.4311264705882323 0.4682217647058806 0.5701882352941183 T T T
0.4433052941176499 0.4992605882352947 0.4148052941176488 T T T
0.5721194117647030 0.5001641176470599 0.3701200000000000 T T T
0.4320752941176451 0.4726094117647079 0.6279252941176452 T T T
0.5677594117647047 0.5357800000000026 0.6020994117647049 T T T
###############################################################
As k-point I am using the Gamma point as I am dealing with a single molecule in a big box.
I would be very grateful is someone could help with an advice on how to properly obtain the values for the dipole moments. According to the manual and to the forum the IDIPOL = 4 setting should be sufficient for a vacuum molecule. Have I missed something ?
With all my best wishes,
Eduard