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Getting started

Relativistic calculation: Using the PySCF Interface

Guidelines to write input file of Ground State Energy in the relativistic framework:

While writing the input file, one should write which method is following; it doesn’t matter whether it is lower case or upper case. For a relativistic framework, if the interface is pyscf, one should write spinor. After that, you should write the desirable basis-set; if the bond lengths are in Angstrom, there is no need to write anything else you have to write Bohr at the end if it is not in the Angstrom unit.

Example:

! method interface basis-set

%cc
------
------
------
end

*xyz charge  multiplicity
A x1 y1 z1
B x2 y2 z2

In %cc block, which desired incore should mentioned for integrals, if the molecule is linear, then the real_ints True sentence should written. The coupled cluster convergence tolerance should be mentioned for the desired accuracy using cc_convergence keyword. The coordinates you are working with should be mentioned in the next line (*xyz), along with the charge and multiplicity. After that, the coordinates of the molecule need to be mentioned in the cartesian co-ordinates with proper atomic symbols ( A, B ).

For example a four-component relativistic coupled cluster singles doubles (CCSD) calculation using pyscf interface can be performed using the following input file,

! CCSD spinor unc-ccpvdz Bohr

%cc
incore 5
real_ints True
cc_convergence 1e-7
end

*xyz 0 1
H 0.0 0.0 0.0
F 0.0 0.0 1.7325

Here,

CCSD : name of the method

spinor : pyscf inference in relativistic framework

unc-ccpvdz : basis-set

Bohr : unit of bond lenght

incore 5 : desired incore for integrals

real_ints : For linear molecules, it is preferable to use True

cc_convergence 1e-7 :tolerance of CCSD converegnce

*xyz : Cartesian coordinate

0 : charge of the molecule

1 : spin multiplicity (2S+1)

H,F : Atomic symbols

Non-relativistic calculation: Using the PySCF Interface

Guidelines to write input file of Ground State Energy in the non-relativistic framework:

The input file for a non-relativistic framework is nearly identical to that for a relativistic framework. For a non-relativistic framework, if the interface is a pyscf spin-adapted implementation, then there is no need to write anything regarding the interface in the input file.

Example:

! method  basis-set unit

%cc
------
------
------
end

*xyz charge  multiplicity
A x1 y1 z1
B x2 y2 z2

The %cc block is also similar to the relativistic one, with the change that’real_ints ‘’true’’ should not be present. For example a non-relativistic coupled cluster singles doubles (CCSD) calculation using pyscf interface within spin-adapted implementation can be performed using the following input file,

! CCSD unc-ccpvdz Bohr

%cc
incore 5
cc_convergence 1e-7
end

*xyz 0 1
H 0.0 0.0 0.0
F 0.0 0.0 1.7325