Hello Soumyadip Ray,

In GAMESS (General Atomic and Molecular Electronic Structure System), spin-orbit coupling (SOC) calculations can be performed using the Relativistic Effective Core Potentials (RECP) or the Two-Component Spin-Orbit (SO) method. I'll provide an example of input for each method:

RECP Method:

For RECP calculations, you need to include the ECP and SO in the input. Here is an example of a simple input for a TlH molecule using the RECP method:

==============================================

$CONTRL SCFTYP=RHF RUNTYP=ENERGY ECP=RECP $END

$SYSTEM MWORDS=4 $END

$BASIS GBASIS=ECP ECP=TlH $END

$GUESS GUESS=HUCKEL $END

$SOINT XTYPE=RECP $END

$DATA

TlH molecule with RECP

C1

Tl 81.0 0.000000 0.000000 0.000000

H 1.0 0.000000 0.000000 1.900000

$END

==============================================

Two-Component Spin-Orbit (SO) Method:

For the Two-Component Spin-Orbit method, you need to include the DFT and SO in the input. Here is an example of a simple input for a TlH molecule using the Two-Component Spin-Orbit method:

==============================================

$CONTRL SCFTYP=RHF RUNTYP=ENERGY DFTTYP=B3LYP $END

$SYSTEM MWORDS=4 $END

$BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=1 DIFFSP=.TRUE. $END

$GUESS GUESS=HUCKEL $END

$SOINT XTYPE=AMFI $END

$DATA

TlH molecule with Two-Component Spin-Orbit

C1

Tl 81.0 0.000000 0.000000 0.000000

H 1.0 0.000000 0.000000 1.900000

$END

==============================================

In both examples, the input file starts with the $CONTRL group specifying the calculation type, followed by the $SYSTEM group for memory allocation. Then, the $BASIS and $GUESS groups define the basis set and initial guess, respectively. The $SOINT group specifies the spin-orbit coupling calculation type, and finally, the $DATA group provides the molecular geometry.

Please note that the basis set and other options might need to be adjusted depending on your specific system and the level of theory you want to employ.

Regards,

Alessandro

Alessandro Rizzo I have tried with your input. However, it is showing.

ERROR, NO $DATA GROUP WAS FOUND

This type of error. I have no idea about Gamess, please help.

Soumyadip Ray The error message you received suggests that the $DATA group is not being recognized, which is essential for providing the molecular geometry. Here's a quick troubleshooting guide:

Make sure there is no space between the dollar sign ($) and the keyword (e.g., $DATA).

Ensure that each group is separated by a line break (an empty line) and that there are no extra spaces or characters in the input file.

Verify that the $DATA group is properly formatted, with the correct molecule name, symmetry, atomic symbols, atomic numbers, and coordinates.

To reiterate, here is the corrected input file for the Two-Component Spin-Orbit (SO) Method for the TlH molecule:

==================================================

$CONTRL SCFTYP=RHF RUNTYP=ENERGY DFTTYP=B3LYP $END

$SYSTEM MWORDS=4 $END

$BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=1 DIFFSP=.TRUE. $END

$GUESS GUESS=HUCKEL $END

$SOINT XTYPE=AMFI $END

$DATA

TlH molecule with Two-Component Spin-Orbit

C1

Tl 81.0 0.000000 0.000000 0.000000

H 1.0 0.000000 0.000000 1.900000

$END

====================================================

If you still encounter issues, please provide more details about the error message, and I'll be happy to help you further.

regards,

Alessandro Rizzo

Dear sir,

I am still unable to perform the calculation. I am doing something wrong. I am giving you a random molecule, say Benzene, to clarify my doubts. Here is the geometry:

C 1.71583843 0.76086955 0.00000000

C 3.11099843 0.76086955 0.00000000

C 3.80853643 1.96862055 0.00000000

C 3.11088243 3.17712955 -0.00119900

C 1.71605743 3.17705155 -0.00167800

C 1.01845643 1.96884555 -0.00068200

H 1.16607943 -0.19144745 0.00045000

H 3.66050643 -0.19164345 0.00131500

H 4.90821643 1.96870055 0.00063400

H 3.66108243 4.12927255 -0.00125800

H 1.16593543 4.12933255 -0.00263100

H -0.08114757 1.96902855 -0.00086200

Though I intend to calculate SOC for an Fe complex, but Benzene can be a good example to understand the situation.

What should be the input? In the test files of gamess, exam19.inp (added with it) shows SOC calculation, but it has some ROHF values at the end of the input file. I do not understand how to generate it and what I should grep from the output. Please enlighten me with the abovementioned geometry.

Thanks in advance. Please check the added input file.

Dear Soumyadip Ray,

I understand that you are having trouble setting up the input for a spin-orbit coupling (SOC) calculation in GAMESS using the example of benzene. I will provide you with an example input file for benzene based on your provided geometry. However, I must emphasize that SOC effects are generally more significant for heavier elements like transition metals, and benzene may not be the best example to showcase SOC.

Here is the input file for a simple SOC calculation using the two-component spin-orbit method for benzene:

====================================

$CONTRL SCFTYP=ROHF RUNTYP=ENERGY RELWRT=YES coord=unique units=bohr $END

$BASIS GBASIS=N31 NGAUSS=6 $END

$SCF DIRSCF=.TRUE. $END

$DATA

Benzene

C1

C 6.0 1.71583843 0.76086955 0.00000000

C 6.0 3.11099843 0.76086955 0.00000000

C 6.0 3.80853643 1.96862055 0.00000000

C 6.0 3.11088243 3.17712955 -0.00119900

C 6.0 1.71605743 3.17705155 -0.00167800

C 6.0 1.01845643 1.96884555 -0.00068200

H 1.0 1.16607943 -0.19144745 0.00045000

H 1.0 3.66050643 -0.19164345 0.00131500

H 1.0 4.90821643 1.96870055 0.00063400

H 1.0 3.66108243 4.12927255 -0.00125800

H 1.0 1.16593543 4.12933255 -0.00263100

H 1.0 -0.08114757 1.96902855 -0.00086200

$END

====================================

This input file will perform a restricted open-shell Hartree-Fock (ROHF) calculation with the two-component relativistic method. Note that this calculation may not showcase significant SOC effects due to the absence of heavy atoms in benzene.

For an Fe complex, the input setup would be similar, but you would need to include the geometry of the Fe complex and might need to choose a suitable basis set and methods for the specific system. Also, if you are interested in SOC for excited states, you will need to set up a multi-reference or multi-state calculation in addition to the two-component relativistic method.

I hope this helps you to get started with your SOC calculations in GAMESS. Good luck!