modify comment, doumentation and HSE example INPUT

Author: wenfei-li

docs/input-main.md

@@ -210,40 +210,33 @@ This part of variables are used to control general system parameters.
 #### dft_functional
 
 - **Type**: String
-- **Description**: In our package, the XC functional can either be set explicitly using the dft_functional keyword as explained below, or set implicitly according to the XC functional information read from pseudopotential file. The user should ensure that the XC functional set in the INPUT file and the pseudopotential file are consistent. If more than one element is present in the system, make sure all of pseudopotentials have the same XC functional. **Currently only LDA and GGA are supported.**
-
-    To be specific, we briefly explain the format of the pseudopotential file and the key information it contains. There are a few lines in Si`s GGA pseudopotential file Si_ONCV_PBE-1.0.upf:
-
-    ```
-    ...
-    <PP_HEADER
-    generated="Generated using ONCVPSP code by D. R. Hamann"
-    author="Martin Schlipf and Francois Gygi"
-    date="150105"
-    comment=""
-    element="Si"
-    pseudo_type="NC"
-    relativistic="scalar"
-    is_ultrasoft="F"
-    is_paw="F"
-    is_coulomb="F"
-    has_so="F"
-    has_wfc="F"
-    has_gipaw="F"
-    core_correction="F"
-    functional="PBE"
-    z_valence=" 4.00"
-    total_psenergy=" -3.74274958433E+00"
-    rho_cutoff=" 6.01000000000E+00"
-    ```
-
-    Possible values of this variable are:
-  - none: the functional is specified implicity by the input pseudopotential file
-  - lda: Perdew-Zunger local density approximation
-  - pbe: Perdew-Burke-Ernzerhof general gradient approximation
-
-    If the functional specified by the user is not consistent with the pseudopotential file, the program will stop with an error message.
-- **Default**: none
+- **Description**: type of exchange-correlation functional used in calculation. If dft_functional is not set, the program will adopt the functional used to generate pseudopotential files, provided all of them are generated using the same functional. For example, we present a few lines in Si’s GGA pseudopotential file Si_ONCV_PBE-1.0.upf:
+        ```
+        ...
+        <PP_HEADER
+        generated="Generated using ONCVPSP code by D. R. Hamann"
+        author="Martin Schlipf and Francois Gygi"
+        date="150105"
+        comment=""
+        element="Si"
+        pseudo_type="NC"
+        relativistic="scalar"
+        is_ultrasoft="F"
+        is_paw="F"
+        is_coulomb="F"
+        has_so="F"
+        has_wfc="F"
+        has_gipaw="F"
+        core_correction="F"
+        functional="PBE"
+        z_valence=" 4.00"
+        total_psenergy=" -3.74274958433E+00"
+        rho_cutoff=" 6.01000000000E+00"
+        ```
+    According to the information above, this pseudopotential is generated using PBE functional.
+    On the other hand, if dft_functional is specified, it will overwrite the functional from pseudopotentials and performs calculation with whichever functional the user prefers. We further offer two ways of supplying exchange-correlation functional. The first is using 'short-hand' names such as 'LDA', 'PBE', 'SCAN'. A complete list of 'short-hand' expressions can be found in [source code](../source/module_xc/xc_functional.cpp). The other way is only available when ***compiling with LIBXC***, and it allows for supplying exchange-correlation functionals as combinations of LIBXC keywords for functional components, joined by plus sign, for example, 'dft_functional='LDA_X_1D_EXPONENTIAL+LDA_C_1D_CSC'. The list of LIBXC keywords can be found on its [website](https://www.tddft.org/programs/libxc/functionals/). In this way, **we support all the LDA,GGA and mGGA functionals provided by LIBXC**.
+    We also provides (under test) two hybrid functionals: PBE0 and HSE. For more information about hybrid functionals, refer to the [section](#exact-exchange) on its input variables.
+- **Default**: same as UPF file.
 
 #### pseudo_type
 
@@ -975,6 +968,8 @@ This part of variables are used to control the molecular dynamics calculations.
   - 2: NVT ensemble with Langevin method;
   - 3: NVT ensemble with Anderson thermostat;
   - 4: MSST method;
+  
+  ***Note: when md_type is set to 1, md_tfreq is required to stablize temperature. It is an empifical parameter whose value is system-dependent, ranging from 1/(40\*md_dt) to 1/(100\*md_dt). An improper choice of its value might lead to failure of job.***
 - **Default**: 1
 
 #### md_nstep

examples/hse-Si-example/INPUT

@@ -13,11 +13,10 @@ smearing_method   				smearing_method
 mixing_type				pulay
 
 dft_functional			hse
-exx_separate_loop		0		
-exx_pca_threshold		1E-3
-exx_ccp_rmesh_times		10
-exx_c_threshold			1E-4	
-exx_dm_threshold		1E-3	
-exx_schwarz_threshold	1E-4	
-exx_cauchy_threshold	1E-6	
-
+exx_separate_loop 1
+exx_pca_threshold 1e-4
+exx_c_threshold 1e-4
+exx_dm_threshold 1e-4
+exx_schwarz_threshold 1e-5
+exx_cauchy_threshold 1e-7
+exx_ccp_rmesh_times 10

source/module_xc/xc_functional.cpp

@@ -19,15 +19,18 @@ int XC_Functional::get_func_type()
 // for detail, refer to https://www.tddft.org/programs/libxc/functionals/
 void XC_Functional::set_xc_type(const std::string xc_func_in)
 {
+    //Note : due to the separation of gcx_spin and gcc_spin,
+    //when you are adding new GGA functionals,
+    //please put exchange first, followed by correlation,
+    //such as for PBE we have:
+    //        func_id.push_back(XC_GGA_X_PBE);
+    //        func_id.push_back(XC_GGA_C_PBE);
+    
     func_id.clear();
     std::string xc_func = xc_func_in;
     std::transform(xc_func.begin(), xc_func.end(), xc_func.begin(), (::toupper));
 	if( xc_func == "LDA" || xc_func == "PZ" || xc_func == "SLAPZNOGXNOGC") //SLA+PZ
 	{
-        // I should use XC_LDA_X and XC_LDA_C_PZ here,
-        // but since we are not compiling with libxc as default,
-        // I chose to set it manually instead.
-        // Same for the rest.
         func_id.push_back(XC_LDA_X);
         func_id.push_back(XC_LDA_C_PZ);
         func_type = 1;