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.