When configuring SharePoint 2013 in “Complete” mode you get a “The username is invalid. The account mist be a valid domain account” when using a local account to configure the farm…
Out of the box SharePoint only supports “Stand-alone” mode for non domain environments, but this forces you to use SQL Server 2008 R2 Express Edition which is most cases is unacceptable.
The solution is to use a PowerShell command to create the initial configuration of the farm with a local account:
1) Start the SharePoint PowerShell (not the "standard" one)
2) Run “New-SPConfigurationDatabase” from the command line and follow the instructions. This will create the farm and configure the necessary accounts.
3) Rerun the Configuration wizard. After it finishes start the Config Wizard (interactive or not) and configure your server with all components
