input-sections/QM.md

@@ -12,7 +12,9 @@ The `QM` section handles the reference and ChronusQ job type specification. **Th
 | ------- | ---- | ----------- | ------- | -------- |
 | `REFERENCE` | String | Type of reference wavefunction | N/A | Yes |
 | `JOB` | String | Type of calculation | N/A | Yes |
-| `X2CTYPE` | String | Type of X2C transformation | `FULL` | No |
+| `X2CTYPE` | String | Type of X2C transformation | `DEFAULT` | No |
+| `ATOMICX2C` | String | Type of Atomic X2C transformation | `OFF` | No |
+| `SPINORBITSCALING` | String | Type of spin-orbit scaling technique | `DEFAULT` | No |
 
 ### The `REFERENCE` Keyword
 
@@ -24,7 +26,7 @@ REFERENCE = [ REAL/COMPLEX ] <R/RO/U/G/2C><HF/FUNCTIONAL>
 
 The `REAL/COMPLEX` specification is optional, and a canonical choice will be chosen for the user should it not be specified (`COMPLEX` for 2-Component / GIAO references, `REAL` otherwise). The second two keyword fields in the above template are required, and may be combined freely.
 
-`R/RO/U/G/X2C` specifies the desired spin symmetry of the reference wave function: Restricted (S<sup>2</sup> eigenfunction, even number of particles), Restricted Open (S<sup>2</sup> eigenfunction, any number of particles), Unrestricted (S<sub>z</sub> eigenfunction), Generalized (2-Component, no spin symmetry), X2C ("Exact" 2-Component Relativistic, with one-body spin-orbit coupling, no spin symmetry), respectively.
+`R/RO/U/G/X2C` specifies the desired spin symmetry of the reference wave function: Restricted (S<sup>2</sup> eigenfunction, even number of particles), Restricted Open (S<sup>2</sup> eigenfunction, any number of particles), Unrestricted (S<sub>z</sub> eigenfunction), Generalized (2-Component, no spin symmetry), X2C (deprecated, "Exact" 2-Component Relativistic, with one-body spin-orbit coupling, no spin symmetry), respectively.
 
 `HF` will generate a Hartree-Fock wave function, and `FUNCTIONAL` is a place holder to specify a Kohn-Sham wave function with the `FUNCTIONAL` DFT functional. (See below) **`RO` is currently only compatible with `HF`, not Kohn-Sham.**
 
@@ -66,13 +68,34 @@ When the reference is specified as `X2C`, different methodologies can be used to
 
 | Value | Description |
 | ----- | ----------- |
-| `FULL` | The standard X2C transformation algorithm without local approximation |
+| `OFF` | Turns off X2C |
+| `ONEELECTRON`/`ONEE` | The standard core-Hamiltonian X2C transformation algorithm |
+| `SPINFREE` | One-electron X2C, but only include scalar relativistic effect |
+| `FOCK` | X2C transformation based on the four-component Fock matrix |
+| `DEFAULT` | `ONEE` in case of `x2c` reference, `OFF` otherwise. |
+
+### The `ATOMICX2C` Keyword
+
+When the `X2CTYPE` keyword is specified as `SPINFREE` or `ONEE`, either a standard molecular X2C transformation is performed, or local approximations can be utilized. The following options control the types of local approximation.
+
+| Value | Description |
+| ----- | ----------- |
+| `OFF` | The standard X2C transformation algorithm without local approximation |
 | `ALH` | Atomic local approximation to the Hamiltonian |
 | `ALU` | Atomic local approximation to the transformation matrix |
 | `DLH` | Diagonal local approximation to the Hamiltonian |
 | `DLU` | Diagonal local approximation to the transformation matrix |
-| `SO` | Include spin-orbit relativistic effect in X2C |
-| `SCALAR` | Only compute scalar relativistic effect in X2C |
+
+### The `SPINORBITSCALING` Keyword
+
+When the reference is specified as `X2C`, different methodologies can be used to artificially include the two-electron spin-orbit effect. The `SPINORBITSCALING` keyword switches such scaling.
+
+| Value | Description |
+| ----- | ----------- |
+| `NOSCALING` | Turns off two-electron spin-orbit scaling |
+| `BOETTGER` | The Boettger factor scaling technique |
+| `ATOMICMEANFIELD`/`AMFI` | Atomic mean-field two-electron spin-orbit effect |
+| `DEFAULT` | `BOETTGER` in case of one-electron spin-orbit X2C calculation, `NOSCALING` otherwise. |
 
 ## Examples