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#1 2018-04-26 16:59:15

Sarah
Member
Registered: 2016-08-01
Posts: 21

Electric field

Dear all,

I need to apply an electric field (let's say an IR field) to my dimer which is electronically excited, to mimic an experiment. I would appreciate if someone could provide me with an input sample.

What I understand from the Molcas manual 8.2, P. 202:

1. I should use &FFPT option right after &SEWARD, so far so good; then there are two possibilities: DIPO and EFLD >>>> Which one is practical for my purpose?

2. DIPO is followed by the component of the dipole operator (X, Y, or Z... yoop, crystal clear) and the perturbation length >>>> what perturbation length should be used for my purpose?

3. EFLD, here in addition to perturbation length, it is unclear to me how to specify coordinates of the origin.

Valera and Per. A have applied an electric field in their paper (https://doi.org/10.1080/00268976.2012.697587).

Thanks in advance

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#2 2018-04-27 08:12:37

Ignacio
Administrator
From: Uppsala
Registered: 2015-11-03
Posts: 558

Re: Electric field

Sarah wrote:

2. DIPO is followed by the component of the dipole operator (X, Y, or Z... yoop, crystal clear) and the perturbation length >>>> what perturbation length should be used for my purpose?

I guess DIPO is used if you actually want to compute the dipole moment by doing numerical differentiation with respect to the external field strength. The "perturbation length" would be the strength used for the perturbations.

3. EFLD, here in addition to perturbation length, it is unclear to me how to specify coordinates of the origin.

My guess again:

EFLD
X
5.2
ORIG 0.0 0.0 0.0

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#3 2018-04-27 09:58:11

Sarah
Member
Registered: 2016-08-01
Posts: 21

Re: Electric field

Dear Ignacio,

Thanks a lot for your prompt reply,

I followed your instruction, here is how my input looks like:

>> export MOLCAS_MEM = 5072
&gateway
 XBAS = ANO-L-VTZP
 ZMAT
C1
O2      1       1.21550032
H3      1       1.09527166      2       121.32472109
H4      1       1.09447643      2       120.95120860    3       180.0000000     0
End  of  z-matrix
&SEWARD
&FFPT
  EFLD
  X 5.2
  ORIG 0.0 0.0 0.0

and I got the following error

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

      The following tasks will be executed:
      -------------------------------------

      FFPT    EFLD    COMP    COMP0   X= 5.200000
                      ORIG    ORIG0   X= 0   Y= 0   Z= 0

 PtEfld: You missed to specify the origin of the operator.
--- Stop Module:  ffpt at Fri Apr 27 10:41:59 2018 /rc= _INTERNAL_ERROR_ ---
Non-zero return code - check program input/output
--- Stop Module:  auto at Fri Apr 27 10:41:59 2018 /rc= _INTERNAL_ERROR_ ---

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#4 2018-04-27 10:09:37

Ignacio
Administrator
From: Uppsala
Registered: 2015-11-03
Posts: 558

Re: Electric field

Try specifying origin coordinates that match exactly those of some atom. It probably has to be done in atomic units, so it would be best to actually change the geometry such that the desired atom is at 0,0,0.

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#5 2018-04-27 10:33:22

Sarah
Member
Registered: 2016-08-01
Posts: 21

Re: Electric field

I changed the geometry so that my Carbon is at 0, 0, 0:

&gateway
 coord
 6
Title Card Required
C    0.000000    0.000000    0.000000
O    0.000000    0.000000    2.296963
H    1.768064    0.000000   -1.076045
H   -1.773752    0.000000   -1.063723
 Basis=ANO-L-VTZP
 group=C1
&SEWARD
&FFPT
  EFLD
  X 5.2
  ORIG 0.0 0.0 0.0

And I get the exact same error:

      The following tasks will be executed:
      -------------------------------------

      FFPT    EFLD    COMP    COMP0   X= 5.200000
                      ORIG    ORIG0   X= 0   Y= 0   Z= 0

 PtEfld: You missed to specify the origin of the operator.

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#6 2018-04-27 15:18:24

nikolay
Member
From: Stuttgart
Registered: 2016-03-21
Posts: 24

Re: Electric field

The error is fixed if one adds

EFLD
0

to gateway, such that the respective integrals are computed.

The problem is that no output is produced with happy landing (at least for me).

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#7 2018-04-27 17:34:46

Sarah
Member
Registered: 2016-08-01
Posts: 21

Re: Electric field

Dear Nikolay,

Thanks! adding EFLD 0 to gateway worked for me and I have a happy landing output. I would be more than happy if I could help you to get a happy output.

one more thing:
I still don't get the "perturbation length" thingy and why Ignacio suggested 5.2 for IR?

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#8 2018-04-28 19:08:57

Ignacio
Administrator
From: Uppsala
Registered: 2015-11-03
Posts: 558

Re: Electric field

I just used 5.2 as a random number. I presume "perturbation length" is the field strength. If you want an IR field, you probably want a time-dependent perturbation, I don't know if you can add this with FFPT.

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